Body shops charge by the hour. It takes a lot of man hours to remove all the stainless trim that surrounds the sail. To get the top crossover above the rear window off requires removing the rear portion of the headliner. To do that requires removal of interior trim pieces. You might consider just removing the trim piece that holds the courtesy light and using a hole saw cut a piece out of the C pillar to access those two nuts. It would require two holes on each side (inner and outer) but with careful planning and some finesse would be a lot less time consuming.