You can find this exercise on page 135 of the book Synergistic Golf.
Exercise Type: BIG BALL
Exercise Category: FLEXIBILITY, HIPS, LOW BACK
Sit on top of ball with feet hip distance apart and directly under knees. Keep upper torso and head still. Rotate hips on ball in clockwise motion 10x then repeat counterclockwise 10x. Sit tall and elongate spine throughout movement.