Whip, the section of foreshaft where the stone point would go would be the full diameter of the wood shaft. About an inch below the notch for the point, the wood shaft would smoothly taper to the OD of the carbon shaft. Then there would be two or three inches of the wooden foreshaft turned to the inside diameter of the carbon shaft.
30coupe, I think you're probably right that cedar wouldn't be strong enough. I think I'll try, though. :D Also have some hardwoods around here to play with.