For the piano shot, which I am currently animating, the Alex rig needed full freedom of movement in her fingers so she could stretch to her fingers to reach certain notes. Initially, the fingers could bend, but they could not spread out. Equally, the thumb could bend in but could not tap. To resolve this I quickly created two drivers in each of the wrist controls, Thumb Tap and Finger Spread. These attributes were set to drive the rotation of the joints in the fingers.