I'd need to get one of Camp's cargo nacks to keep it in, but I think that would work

 

Steel plate bolted or welded to the floor, with studs/bolts welded to the steel plate that line up with the the holes in the wheel. Then secure it with some of those locking lug nuts that require a special key socket to take off. I don't know if you can picture that or not

 

you could get that tuffy security deck and just slide the tire underneath it...

 

OHH you just gave me an idea! how about you just take a spare tire carrier like the stock one but without the third brake light where its just the round carrier (if you can find a steel one go with that) and bolt (or weld if you find a steel one) the round tire carrier for the rear gate to your jeep floor and then mount the tire on there as if it were on the rear gate and use three or however many locking lugs it holds to hold it down

 

Yeah... I was out looking at the spare tire carrier earlier and realized the same thing. Just take a reciprocating saw and cut the third brake light off