Came up with another single-hole bushing concept - this one is very easy to make using inexpensive PVC fittings that cost about 80 cents.
A 1/2" threaded male adapter and a 1/2" threaded cap.
Cut down the adapter, and drill a 3/8" hole in the cap.
A little sanding to smooth off the adapter...
Voila! Mini PVC Bushing and retaining nut. Could be painted with Krylon plastic paint.
Assembly, with bungee cord and 1/2 od x 3/8 id polyethylene tubing
Here's the stainless bushing version
This is what each would look like installed in the gunwale, or in a deck lid.
The PVC bushing would need a 3/4" hole, the stainless version would need only a 1/2" hole.
The hook ends that Bill shows would actually retract quite a ways into the PVC bushing I think, assuming the hook's locking ring is 1/2" od.