You can find this exercise on page 254 of the book Synergistic Golf.
Exercise Type: PRE-ROUND WARMUP
Exercise Category: BACK, FLEXIBILITY
Begin standing with club overhead. Perform a slightly inward pull of the abdominals to help support spine. Cross your right leg in front of your left leg. Then slowly lean to the right until you feel a gentle stretch. Don't slouch...lift and separate through the ribcage. Hold for about 10 seconds. Repeat with other leg 3 times.