I have found that the above way of making this figure is better than the boil and pop method. This way you can use the actual Stormtrooper neck and not have to paint the Han and Luke necks black. And this way you get a short neck too. That's important so it wont look funny with the helmet on.
***UPDATE(6/16/01):My plan worked! Making the custom figure like I have diagramed lets you keep the up/down articulation in the head, as well as the side to side.