You can find this exercise on page 70 of the book Synergistic Golf.
Exercise Type: BIG BALL
Exercise Category: FLEXIBILITY, LEGS - FEET, LOW BACK
Lie on floor with ball between feet straight in the air. Place palms face down on floor at shoulder height. Squeeze inner thighs toward each other. Engage abdominals and obliques and rotate legs over to the right and rest ball on floor. Try to keep upper body still. Inhale to prepare. Then exhale and raise legs back up to middle. Repeat each way 5x. Bend knees if needed to maximize leverage.