Keeping thermoplastic from sticking to models
I've never used the stuff, but it has a reputation for sticking to everything.  Have you tried a release agent?  I'll offer some speculation on what should probably work (the first things I would try in your situation).

If the shape of the object lends itself, wrap it with oven parchment paper.  That's impregnated with silicone, takes high temperatures, and not much sticks to it.
If you aren't worried about preserving surface detail, dilute silicone caulk with mineral spirits to a thin paint consistency and coat the object with it.  Give it a few days to completely dry and cure.  It won't be very durable, but you may get several uses out of it before you need to peel off the coating and apply a fresh one.
Dust the object surface with powdered graphite or talc.
Coat the object with WD40 unless the solvents will attack the object, in which case, just apply a coating of oil or a thin layer of petroleum jelly (Vaseline).
If the object won't melt or distort, dip it in melted wax and use a hot air gun to melt off all but a very thin layer of the wax.  The hot plastic may melt more of the wax or bond with it, but it should still release from the object.
If you can't get a decent layer of graphite or talc to cover the object, coat the surface with WD40 or oil.  Use that film to hold a good dusting of graphite or talc.

You may need to try a few different things to find what works best on a particular surface.
Another thing that might help release it: stick it in the freezer overnight.  The plastic will become less elastic and you might also get differential shrinkage of the plastic and the object.