This won't help with the repair, but might be of use going forward to take the stress off the seat -
Seat Savers. We used one on our first boat ('98 Cobalt 232) as we had to step on the sunpad to enter the boat, and started to get small tears on a seam or two. (We used superglue to bond it back together. While it did show a bit, it wasn't bad at all.)