You two are on the right track. The boat I use the sock with is fiberglass with no internal structure, and I was too stunned to see the possibilities for your framed boats. You could secure the aft end of the sock, then loop some strings around a forward frame member, pull the whole thing taut and tie it off before fixing it to the coaming. Nice.

That is also a nice idea to use the sock as a boat bag; I just use mine to haul gear in.