Testors modeling putty (in the grey tube, about three bucks) is pretty great for sculpting hair wherever you want to put it. It's about the consistency of cake frosting, so you'll want a dull X-Acto blade to move it around. You can sand it when it's dry, if necessary. I'm NOT sure it will be happy if the head it's on is boiled, so I'd put the head on its final body before starting to sculpt. I have customs using it that are 10-15 years old, and they're still together.
It gets a little whiffy, like marker fumes, so have a fan going in the room.
I have never kissed the editor of the Radio Times