You may be able to separate the skin from the foam by heating it with a propane weed burner as you peel it off. If that doesn't work, then perhaps trying a floor scraper as you peel it back.
If it is anything like the spray foam in my Dina, the foam will burn if exposed to much heat. You would need to be very careful not to apply much heat. The smoke if it does burn is really nasty.
I did a test and tried to burn some foam from something I removed. The foam will start on fire with enough heat, but it doesn't tend to stay burning if the heat source is removed.