You can find this exercise on page 142 of the book Synergistic Golf.
Exercise Type: PRE-ROUND WARMUP
Exercise Category: FLEXIBILITY, LOW BACK, RHYTHM - TIMING
Stand in address position with same hip tilt and spine angle. Rest club parallel with ground across back of shoulders holding on to ends. Inhale prepare. Exhale rotate upper body as if in backswing trying to turn shoulders and club 90 degrees. Pause. Inhale repeat to start. Repeat backswing 10x. Then proceed to follow through on opposite side. Focus on controlled movements.