Rather than mailing his ticket back to the FAA, I suggested the following: Commercial includes private and light sport privileges. Most training gliders fit in light sport. Train to proficiency with one instructor. Fly with a second instructor to add light sport glider via a log book endorsement. This could count as the flight portion of a flight review. Now, the pilot can "solo" the glider as PIC on light sport privileges, rack up 20 solos, a recommendation ride, and after a check ride be a commercial glider pilot.

So, two parts 1) is there some legitimate way around the first part of the issue? and 2) what do you think of the light sport approach if a flight review is required.

If the ultimate goal is an add-on to the Commercial Pilot level, be careful about the Flight Instructor you pick under Sport Pilot rules. If the Flight Instructor was certified under the Sport Pilot rules only, his instruction time with you does not count towards later getting the Commercial Pilot training. You have to run with a non-Sport Pilot-certified Flight Instructor instead.