my first idea is the more simple one. a simple UI on the side of the screen, displaying the tori. using the left analog stick, you can move between selected joints, and use the left and right bumpers and triggers to cycle between joint states (hold/relax for bumpers, extend/contract for triggers)
you could also program the right analog stick for camera movements, although i don't know if that's possible at all.

my next idea is more complex, but would be much more useful for aikido matches and such.
using left and right bumpers, you can select the right and left side of your tori. from there, you can use your d-pad/triggers/analog stick to select certain joints, then press A and B to cycle through hold/relax/contract/extend states. hell, you could use all the four buttons and assign a state to each of them.

for every selection, you could outline the actual joint of the tori, maybe by spawning a cell shading item on the joint selected (no idea if this is possible via simple .lua script or not) regardless, some sort of integration with the game itself, instead of an overlay would be damn neat.