I think, according to your drawing, that the spoke-adjustment-space would overlap the truss rod route. Or, if you're going to route into the neck pocket, the straight truss rod channel that you drew would work fine. With the Music Man guitars (I can't admit I've played any other spoke-adjusting guitars), only the wheel and the little threaded attachment stick out from the neck; none of the actual truss rod sticks out from the neck heel. So your drawing should be spot on, and you should fit the rod in the straight channel so that just the spoke and threads are sticking out. They way I see it, the anchor area is the wood that's right up against the double-nuts, so you want it nice and snug in there.
As for heel adjustment? If you're using a multilam neck, the neck will be plenty strong, especially if the pieces are quartered. I've got a 2-piece neck on one of my guitars, the other two are 1-piece, and I have never had any problems with the headstock adjustment truss rod. And none of them have scarf joints But I know where you're coming from, better safe than sorry. I'd have done it on my own build, if I didn't buy a prefab neck.
So how am I doing, closer to what you're looking for? hahahaha