In the past I have opened them as far as I could, without tearing, then fill with a small amount of epoxy sculpt. Then shape and card as mentioned. That or cast and mold them.
Jim, your way works as well and a helluva lot cheaper. The best small game guy who ever lived was my friend Henry Wichers Inchemuk and in his article on squirrels, he says he only carded them.
BTW Allie, the older I get, the better I was. I should hope that you, one day will reach that age. It allows what memory you do have to provide help for those willing to take it.