Plastic head temperature threshold

[Natedog]

I'm looking at possibly sculpting a helmet onto a plastic hasbro head using sculpy. Since the sculpy needs to be cured at 275°F I'm assuming at those temps the head would melt. Has anyone attempted something like this. Any suggestions? Any tips for removing the uncured sculpted helmet from the head without ruining it so you can can bake it?

 

[Collectorcol]

Make a wax mould of the head, Sculpt the helmet to the wax, Bake it and wax melts

Wow! I'm a genius! Never sculpted anything, or considered it, in my life
Maybe I should start

 

[Dubby]

I boil sculpy in water, not sure if that might be a better option?