Why will it have "short-grain"? If the wood you're using has a curve in the grain at the junction, just use it to your advantage. (My tele has continuous grain right through that area - the grain aligns perfectly with the headstock as it comes in - but it's all straight). But in your case, angle the headstock just enough for continuous grain from the main part of the neck to the headstock. It's never going to be an actual Fender. If the required angle is still shallow, you may still need a string tree (or two), but that's NBD.