I soaked mine in a jar of denatured alcohol for a few weeks. I think that was about 3 years ago, and I still used them this halloween. I used marbles and fishing line to pose their feet. After they soaked I just took them outside a left them to dry for a while. I think the skin turned out...
I love, love, love my guineas! They are pushy and loud, they sometimes pick on my chickens. Regardless they are really fun to have, and I haven't had to pick a tick off of anything in years!