Your idea is good jpbouza, but what if you want the IK on but the stretch off? If the stretch is constrained to the IK you will be unable to do so.
I would recommend constraining the location (and rotation if the switch travels with the rig) of the stretch switch to a dummy bone. Then drive the location constraint with the IK switch… so when the IK is on, the constraint is off, but when the IK is off, the constraint is on (locking the stretch switch at 0).
I’ve attached an example to show you, because I don’t actually consider this to be easy :rolleyes:
Try moving the red control bone way off to the side, then play with the switches. The stretch applied only to the forearm is not very useful of course, I just made it simple and quick for demo purposes.
switchingSwitches.blend (161 KB)