Dear Lazyweb, I need a replacement ice maker for my fridge that accepts two-piece ice molds, so that I can cool my drinks with the skulls of my enemies on demand. I can't be expected to keep filling these ice molds by hand, like an animal. Go, make a Kickstarter or something. Go.
Hmm, your enemies in particular?
Unless these enemies are obliging enough to email you CAT scans, first step would be to modify one of the 3D libraries that turns photos into 3D models. We'd want a guess at the underlying bone structure rather than the surface, one of those CSI/Bones magic facial reconstruction programs running in reverse.
How many skulls per day? (Per hour?) For high volume a 3D printer would generate the molds, assuming there's one where the plastic being extruded doesn't break when frozen. For the low volume personal touch "today I want to cool my drinks with the skull of this guy" maybe a custom 3D printer that sprays water into a below zero chamber to create ice sculptures?
Yeah I'm nerding out :-)