I like the thinking exercise. Perhaps a tube (Yost style) construction where the gunwale tubes aft of the cockpit are able to slide into one another. Then the deck ridge (center, topside) aft is a single tube which could pivot via a pin at both ends. This deck ridge would keep the overal length constant while allowing the gunwales to expand and contract. Now the hard part... foot pegs that pivot with cables attached via pullies to mounting points on the gunwales 3/4 of the way down towards the stern.
Not much extra added weight. Just a thought, feel free to shoot it down.
Tim

: It's largely a thinking exercise. Everyone here is a craftsman, tinkerer,
: designer and engineer, to some degree. I'm thinking of something
: Yost-like, or other, as opposed to messing about with traditional design.
: Obviously, the appeal of applying this notion to SOF is the flexibility.