You can find this exercise on page 301 of the book Synergistic Golf.
Exercise Type: DB STRENGTH
Exercise Category: CLUB CONTROL - ACCURACY, POSTURE, RHYTHM - TIMING, SHOULDERS, STRENGTH
In wide stance, hold 3-5-8lb weight in right hand, same arm in top position. Bring right elbow past right hip, shift body weight to left keeping hand with weight back. At the impact position, bring weight down across, and bending knees, reach across left foot. Repeat 20-30x with control.