Personally, I would avoid thinking so much of making a circular/scooped shape, since I think he will end up with the same problem. I would mark off 4" for the handle, and for now just make a more-or-less straight line to the thickest remaining part of the limb. It can be scooped and shaped a bit as tillering progresses. I'm not sure how long the handle is now, so this is a rough guess, but something like this picture maybe.