You can find this exercise on page 105 of the book Synergistic Golf.
Exercise Type: HEAVY BALL
Exercise Category: ABDOMINALS, LOW BACK, POWER PRODUCTION, STRENGTH
Lie down on back holding ball on chest with legs straight together and toes pointed. Inhale to prepare. As you exhale, roll up reaching ball up toward sky as one leg lifts toward sky as well. Goal is to be able to touch ball to toe of lifted leg. Inhale return to floor and exhale repeat with other side. 20 repetitions total. Focus on rounding spine on the way up and on the way down with control.