I made over a dozen p/m skulls with and without jaws this Fall. I used those plastic skulls from spirit as the master. I used pledge furniture polish sprayed over the master as a release. P/M 'ed right over it , no foil or nothing. Built up about 4 layers mabe more around the eyes and nose. When I removed mine I just cut a line behind the jaw all the way over top to the other side. (two pieces) The back of the skull pops right off and the front needed a little finesse as there are a few high spots to go over. I used the handle of a plastic spoon to use as a "shoehorn" to slip over those spots.
Some slight tearing - but no biggie as you have to rejoin the halves anyway.
I saw those other methods with the three cuts and figured that was too much work putting them back together.