does no one know the powdered milk in the bed sheets trick? It works better when its warmer, but basically the body sweats while sleeping, which disolves the powdered milk, and it then gets into the pores. And yes this does stink rather badly, and does not wash off easily. There is truth to the Mallrat's line 'a small price to pay for the smiting of ones enemy'.
However, honestly, you might just be best off putting up with it. Obviously don't let him walk all over you, and don't put up with his shit, but be quick to hand it back. Another thing to keep in mind if he's using/abusing your stuff, see if you can get a lock-box or a lock and figure out how to lock it up (like in a bureau or something). That way if he breaks into it, you have him for destruction of your property, chances are that doesn't fly.
life is too short to have any regrets