Your suggestion for removing the foam sounds like an evironmental and safety nightmare.

I build a plug on which to build my female mold halves using some of your suggestions, to protect the foam and insure a fine finish I coated it with drywall mud and epoxy paint, which allowed the mold to part from the plug very nicely. I agree with the other writer that mechanically removing the foam would be the way to go, and suggest that coating the plug first would help you.

I also built a nice plaster statue of Buddha this way, and wound up with a nice hollow statue by mechanically picking out the styrofoam armature.