I'm gonna make this suggestion for it's value only. I had a "discussion" about this with a friend recently, and suggested a poly cleat available in most marine places and also Wallyworld. He argued about putting holes in the boat and wouldn't do it. If the right size hole is drilled, caulked and backed with support material so the screws/bolts don't further violate the structural integrity of the boat, then there shouldn't be a problem with making two 1/8" or 3/16" holes in a piece or heat molded flexible plastic. Otherwise, a process is available that alows synthetic materials (plastics)to be welded - actually welded - together - which would allow a poly cleat to be welded to the surface of the boat. AND, short of tying an anchor line to the tether inside my yak, where I tether my extra paddle, etc., I have no other suggestions.
Any further ideas?