The way I've come up with is creating an arm control that only position the ik handle in space and another control that controls the wrist rotation which is placed in a group that is parented in the arm control.
The wrist control group is then constrained to the elbow joint and to the arm control. However this works fine when I switch the constraint in the arm control's default position.
But if I animate the arm control and then want to switch the constraint I get this ugly blend and I then have to counteranimate the wrist control to make it look like it is a fixed switch.
I could animate the blend between a number of frames and key the wrist control in the process, but I'd like it to be simple to animate.
Therefore, what I'm looking for is an expression or a script where you get the values for the wrist control group's rotation before the switch and have it
inserted in the wrist control's rotation values. So you end up with a seemless switch.
I just don't know how to write this. Tried, but given up. I'm guessing you use the getAttr and setAttr attributes, but I can't figure out the rest.