em.down.the.rabbit.hole

May has just been canceled, so 125% it is.

I think employees families would be the first target test cruiser.
A family member has a vested interest in ensuring a positive outcome and it doesn't need to ever become public knowledge until it has occurred.
There are way too many bloggers/vloggers/social media influencers in their own mind who would create clickbait headlines without a care in the world what it might do to the cruise line.  They just want their moment in the spotlight or ad revenue and they will lie and exaggerate to get it.  Not all bloggers are like that but the cruise line doesn't need even one of them on a test cruise.  
Start with employees and family.  That also sends a strong message.  This is safe, we even put our own families on the ship to prove it.

It's coming.  The restart will soon be upon us...

As a solo cruiser I often find points don't post correctly.  When that has happened a quick phone call to Crown and Anchor fixes it.  So far I've never had them decline.
When it comes to any trick or loophole I never know when or if Royal might change the trick or close the loophole.  Consequently I'm hesitant to make it sound likes it written in stone you will always get double points when a cabin mate doesn't board.  You are going around the intent of discounted cabins so its conceivable they *might* one day do something about it.  

As a frequent solo cruiser I am seeing an opportunity right now to book cruises at reduced rates for solo cruisers but the window is closing.  As the restart approaches more and more guests are beginning to see the light and they are starting once again to book cruises.  
 When the restart is announced, even if it starts with just one ship, the floodgates will open and all those hesitant would be cruisers are going to start booking cruises in mass.  At that point the hidden reduced single supplement fares will be eliminated or those few remaining will be consumed quickly.
Right now is a great time for solo cruisers to book but it takes time and effort to find the solo deals.

Right now bookings are at risk due to the pandemic.  My travel agent shared with me that there are reduced single supplement fares to be had but there are capacity controls so the entire ship doesn't book up with just solo cruisers.  
Once the few reduced single fares are gobbled up on that ship and sail date they are gone but it's specific to a sail date.  The next cruise on the same ship might still have them.
Right now there are cruises available with 1x, 1.25x and 1.5x single supplements if you look for them.  I've been busy booking them and so have many other solo cruisers.  Sometimes you watch it disappear right before your eyes so you know another solo cruiser beat you to it.  
If you have flexibility with dates and itinerary or cabin type there are ways to cruise solo without a fake guest and save money. 

What cruise lines often have but don't advertise openly are hidden single supplement reduced fares.  They would rather have every cabin at double occupancy, that is their best case scenario.  When bookings are soft they can sometimes slip in some reduced single supplement fares.  The trick is finding these hidden gems.  A good travel agent helps immensely but you can also come across them yourself from time to time by luck or by pricing a lot of different cruises.  Often they only reduce the single supplement for interior or oceanview cabins but occasionally balconies and suites can be reduced as well.
When Cuba was closed to cruises with zero notice suddenly there were two ships sailing with modified itineraries nearly empty.  They responded with promos to entice booked cruisers not to cancel but many did.    Then they removed the single supplement entirely and boy did I cruise a lot with no single supplement.

The video above has all the relevant information as to why single supplements exist.
Listing yourself twice would raise flags and create issues when you begin to check in for the cruise in the weeks or months before the cruise departs  If a guest with that name and birthdate has already started the online check in process, it's impossible for the same guest to check in a second time.  Ultimately a manifest of passengers is created and sent to government authorities for immigration purposes.  Manifests are also the basis for safety protocols such as ensuring every guest has a seat available in a lifeboat in case of an emergency.  The check in systems would see this glaring mistake and not allow the second duplicate guest to start the check in process. At that point it is caught and they could force the cruise to be repriced for what is really occurring - one guest in that cabin.  Busted.
The fake guest approach using a different name clears these check in hurdles.  You and your made up cabin mate can both check in for the cruise.  On the day of the cruise at the pier when you are boarding it's easy enough to say something like "They had a family emergency, the other guest isn't going to make it" or "I told them not to fly in the day of the cruise but they didn't listen and this morning they missed their flight" or "...the airline cancelled their flight and they aren't going to make it".
My first encounter with this did actually see my cabin mate have a family emergency the day before the cruise.  We fully intended to cruise together, had booked excursions together and made other purchases since it was our intention to cruise together.  When they didn't make it I ended up solo and I was given double points.
Since then the only time I used the fake guest trick was for a guarantee rate that wasn't open for solo cruisers to book. 
Guarantee rates allow the the cruise line to advertise heavily discounted fares essentially at a loss hoping that once those two guests are on board they'll spend money to cover that loss.  Their ship, their rules.

Be sure to take advantage of this trick
 
 

If I'm reading your original post correctly, you have put your own info in as both first and second passengers. While the system may allow that, I don't know if that would get red flagged down the road by someone. It would certainly make it difficult to show up and say your ghost isn't showing up -- the ghost is marked down as you with the same first name, last name, middle initial, address, etc.
@twangster, what is your normal strategy if entering a ghost booking? Presumably has to be a real person so passport info etc can be entered during checkin, but do you just have a random friend who's given you the OK to put them in for ghost bookings, or have you been able to do what @em.down.the.rabbit.hole does and just enter your own info twice?

You need to be primary.  I'm not sure that is absolute but I can imagine not being primary could introduce challenges.  

In short, yes you will get double points, at least it has worked that way so far.  You may also get double the normal points during the current double points promo that expires at the end of September 2022.  That means 4 points per night for solo in a double occupancy cabin or 6 points per night for solo in suite cabin.
Booking a ghost will require you pay taxes and port fees for your ghost that doesn't show up but those will be refunded a few weeks after the cruise completes.
Be aware if the cruise cancels and FCC is offered, the FCC will be issued partially in your name and partially in your ghost's name.  On a future cruise your ghost will need to sail to use "their" FCC.
If you have flexibility the single supplement can vary by ship, sail date and by cabin type.  
It sounds like to you may be looking at a GTY or Guarantee cabin.  These can be capacity controlled for solo cruisers so they often don't allow solo cruisers to book discounted GTY cabin fares.  That may account for the price difference you are seeing.

If you booked by yourself in a double occupancy room and you wanted an alcohol package (I realize you don't, but even if you did) you would buy for just one person.  There wouldn't be the second person on the reservation to buy for, it's not even an option.

The only drink package that requires both persons to purchase is the Deluxe Beverage Package, which is the alcohol package.  If you want the Refreshment or Soft drink package, you can purchase just for yourself.  Shouldn't be a problem in your case since you don't want the alcohol package anyway !!!