Doesn't the Sport Pilot require solo time in the glider prior to the double instructor sign off on the 8710-11? How does he do that without a flight review?
Because when it comes down to the bottom line, he is still a rated pilot doing an add-on, solo time, in an aircraft he is not rated for, even if the rating in Sport Pilot, Private, or Commercial.

Questions still need deeper research.

BillT