As far as I know, Disney doesn't do a background check when they rent the campsite, so no way. If you're gonna rent the site for bennies, then offer the extra bedroom to whomever would have rented the campsite. My guess is it's not ever gonna happen.
Well, let's turn that around then......how about since OP only wants the benefits of a campsite and YOU want to stay there....and someone said that you can have 10 people at a campsite, how about you put OP on your campsite KTTW cards....I'm sure he'd be willing to pay you the $42, or maybe only half since you're sharing. Would you be willing to help him get what he wants, and yet still get what you want...that another family be turned away because OP paid for a site.
But....I'm also having trouble here now with the argument that these campsites are all booked up. Just for giggles, I plugged in an arrival date of next Saturday.....I think everyone will agree that this is the height of the busy season right???? Well, I was shown availablity at a cost of $478 for a week long stay at the campsite from July 12 to July 19. So slightly higher cost than OP's $42, but available.
I also thought back to my friends who camp (I don't) and know that they often go in September when it's a bit cooler, but not too cold for outdoor sleeping. So I checked availablity for Labor Day time.....the Saturday before Labor Day to the Saturday after.....again, available during what is again likely a busy time at Disney. Oh, and the week after that as well. Both of these weeks were $42 a night.
Not sure when OP was planning to go, but if there is availability in the busiest month of the year, when exactly it is so booked up that OP would be denying another family a campsite?? Oh, I'm sure there are times.....but it appears that it's not as if it's so booked up that you need to jump in and get your reservations a year in advance.....two random times, during busy times in the parks, and there is a week long availablity and one is a week from today the other 2 months from today.
So perhaps the argument that you can't get a site is based more on WHEN you want to go than on overall ability. Maybe all OP would be doing is making you change to a different week if even that?

How could you do this and feel good about it? Because you spent money? Just curious to see how you can justify it?
That is the most ridiculous example of comparing apples and oranges that I have ever read. There is absolutely no correlation between what this person proposes to do and my utilizing the campsite I reserve in the way it is intended. Your logic is flawed, but really funny. Thanks for the laugh!