Same as for the trad seat bolts by the look of it. When removing the Plus8 seats I had a small a small Stilson that fitted to hold the bolt head while taking the nut off. It was the rear bolt that was the problem, the front 4 were ok . I replaced them with socket heads.
Try the open ended spanner to jam the bolt head or even a flat screwdriver to jam it. An assistant helps! If no assistant gaffer tape. Get socket head bolts ready to replace the hex heads. The box spanner might work as often slimmer than sockets.
