[drunken monkey]

by hot melt vinyl, are you talking about the stuff that you can get at tiranti's in london (in blue/green and white); the stuff you can simply melt down and re-use?
that stuff takes quite a while to cool and seeing as styrene can warp by just being next to a radiator (or even just boiling water) i wouldn't hold out much hope about it holding it's form when in prolonged contact with the vinyl.

have you though about making a master using something like alginate or even the silicon, then cast a positive then use the hot melt stuff over the new cast?
a bit long winded but saves the original.