You can find this exercise on page 201 of the book Synergistic Golf.
Exercise Type: TOWEL
Exercise Category: CHEST, FLEXIBILITY, SHOULDERS
Stand with feet hip distance apart. Hold towel at ends with both hands behind back. Arms should be straight. Slightly bend at knees then at waist leaning entire body forward. Hang from the waist with head looking between knees. Arms will follow over the back and head weighted by gravity. Allow arms to hang as far as comfortable. Do not force stretch. Slowly return to standing rolling up one vertebrae at a time. Return to start. Repeat 2-3x.