Two thoughts - first, you can always teach an old dog new tricks, you just have to show him why it's worth his time. A pup will learn for any treat, praise, etc. An old dog wants to see some value for his effort.
On the real point, biomechnically it should make no difference whether your bow hand wrist is canted or straight, so long as your draw arm elbow stays in the same plane on your draw.
If you want to experiment with it a little, take, as R.H. says, a light weight bow and draw it with the cant you'd normally use, but envision using your draw arm and hand as simply a hook. That'll force you to concentrate on moving your shoulder blade toward the center of your back and using the back muscles to do it. You can do the same thing with a rowing machine, a cable pull, or wrap a bungee cord around a piece of dowel, anchor the other end and pull the dowel toward you, again using your hands and arms as hooks so you concentrate on pulling your shoulder blades together.
That said, given the level at which you're shooting, I suspect you're already doing that and all the course has changed is that you're now thinking about it instead of simply doing it.