I"d suggest using a plastic sheet like a flexible cutting board. There are also some 3-ring binders with flexible plastic covers that you could use. Cut to fit inside of the damaged area. If you have any doubt about the resin stick, test on the plastic first. Use a bag of foam or rags or a float bag to press the plastic sheet against the repair area. You may have to work the repair in sections because it will be difficult to get all areas backed at the same time.
I did a repair on a wooden racing kayak using 1/8" plywood covered with plastic sheeting. That went on the inside and a piece of saran-wrapped plexiglass on the outside. I trilled holes in the plexi and then drove sheet-rock screws through the kayak deck and the backing plywood. The clear plexi allowed me to see the deck pulled up to a smooth surface (the deck was nearly flat) and the ragged edged were all brought together flush with each other. A variation on that system might work if you have sections that don't come together on a fair curve. You could use wooden battens, say 3/4" square wrapped in masking tape. Get the damaged pieces aligned and held in place with resin first then go on to glass work.
I hope that helps
Chris Cunningham, editor
Sea Kayaker magazine