Hey Scott-

I've done one-off molds like that by using aluminum foil adhered with 3M Artist's Spray Mount Adhesive. It's "repositionable," so you can just pull the foil off with almost no residue when you're done. I've used the Maguire's mold release wax on top of the foil. I tried using petroleum jelly, but it didn't work very well. I use the foil instead of plastic because the wax goes onto the foil nicely. It left a nice uniform surface, but when I put on enough petroleum jelly so that the epoxy didn't stick it left texture in the part I molded. I don't know if butter or lard would be better or worse than petroleum jelly.

Having done it both ways, I think that the wax is worth it. It's easy and gives perfect results.

m