You can find this exercise on page 20 of the book Synergistic Golf.
Exercise Type: HEAVY BALL
Exercise Category: ABDOMINALS, LOW BACK, POWER PRODUCTION, RHYTHM - TIMING, STRENGTH
Sit with bent knees keeping toes on the floor. Lean back with a rounded back continually drawing in belly button to spine. Hold heavy ball in center and rotate left and right lightly tapping ball to the floor on either side. Repeat 30 times. Exhale each side.