You can find this exercise on page 250 of the book Synergistic Golf.
Exercise Type: BIG BALL
Exercise Category: FLEXIBILITY, LEGS - FEET, LOW BACK
Lie on floor with legs draped over ball. Ball should be close to hips. Arms outstretched to side, rotate hips and legs back and forth over ball. This is a stretch, not a strengthening exercise. Repeat 10x each side. Focus on relaxed breath.