I'm not sure what you're asking about casting it exactly... If you want to cast it, you just do, but at the same time you'll be working with a very delicate hollowing project nonetheless.
If you're meaning casting a hollow cast of the head, it's possible with the right equipment or with the right experience in doing it by hand. With patience and such you can create incredibly thin, hollow casts, and do so by hand, but it takes patience and practice. 2-part molds to do hollow items tend to be tricky, but they're possible... It's de-airing the cast that's going to give you fits.