Dry ice definitely works on some cars. Every manufacturer probably uses something slightly different, so what works on one car won't work on another.

I used it on the 240sx we're building for LeMons. Break the ice up, spread it around on the sound deadener, cover it with a piece of cardboard, set some weight on it (a couple hammers is what I used), and wait 10 minutes. Clear all the ice off, and smack it with a hammer. The stuff popped right off. I'd guess we removed close to 20 lbs from that car, judging from the weight of the trash bag we tossed it all in.