You can find this exercise on page 307 of the book Synergistic Golf.
Exercise Type: HEAVY BALL
Exercise Category: BALANCE, CHEST, POSTURE, SHOULDERS, STRENGTH
Place both hands on ball: thumbs facing forward and fingertips aiming downward. Lift into plank position with legs straight and feet together. Maintain regular breathing engaging chest and entire midsection. Goal is to be able to hold position for 30 seconds. Extra challenge: lift one foot off floor.