[Spinnaker]

I suppose the reason they want it on the back of the car is to confirm that you have a valid permit that they can check easily while patrolling the parking lot. Ask the security people if you can put it on the windshield and park with the front of the car facing out so they can see the sticker. Tell them why you want to do this and how much a new plastic window costs. All they want is to easily confirm that you have a sticker without having to get out and walk around to the front of your car. It never hurts to ask.
If that doesn't work for them, then I would get some thin clear plastic sheet and put the sticker on that. Tape it to the rear window with some tape that has easily to remove adhesive. Most tape adhesives are easily removed with mineral spirits (paint thinner). Do not use lacquer thinner, acetone, or ketone, or you will need a new rear window. Unless you know how aggressive the adhesive is on the sticker, I wouldn't put it directly on the plastic window. It is too easy to damage it because of the softness of the plastic.
I just had another idea. Tell them that putting it on the windshield and parking with the front of the car facing out is better. If you put it on the rear window and park with the top down, they wouldn't be able to see it.