Pat Lillich has written a tutorial for sculpting jointed hands for a large doll (BJD). She's using Paperclay and Polystyrene tubes to create the hollow finger units (and add strength).
Part 1. Fingers
http://www.shadows.4oni.com/blog/?page_id=121
Part 2. Palm & Stringing
http://www.shadows.4oni.com/blog/?page_id=149
