You can find this exercise on page 153 of the book Synergistic Golf.
Exercise Type: TOWEL
Exercise Category: FLEXIBILITY, LOW BACK, RHYTHM - TIMING
Stand in address position holding ends of towel in both hands parallel to body as if holding it on top of ball path. Inhale to prepare. Head should remain still and stable as if eyes stay on ball. Exhale and pull with right hand and bring arms back as if in backswing. Inhale back to center and repeat other side as if in follow through. Swing with core control keeping head still 10-20 repetitions.