Today, I duplicated the skeleton to make an IK or Inverse Kinematic version and an FK or Forward Kinematic version. I hid the FK version and left it for later. Start the IK feet exactly like you would a Bipedal rig. Create a reverse foot setup by making a separate joint chain starting at the heel, going to the toe, ball and ankle in a revers direction from you IK joint chain. Hide these, we will use them soon. Next, create a Rotation Plane IK Handle from the shoulder to the ankle and two Single Chain IK Handles from the ankle to the ball and from the ball to the toe. Un-hide the reverse feet. You can choose to parent or parent constrain the IK Handles to the corresponding reverse feet joints. I chose to parent constrain just because it keeps the systems separate. Make sure you save now as any testing of the reverse feet before a pole vector is in place may cause shifting of joints.
