Ah interesting this is something I want to figure out for when I install a staysail. I was planning to make some dyneema "tracks" that anchored between the fwd lower chain plate across the cabin top to the other fwd lower chain plate, with loops every couple of inches to have adjustable car positions. I wanted to use soft shackles for attaching everything. You can integrate a frictionless ring with a softshackle so you can move the "car" in board or outboard. Leech tension would be tricky to adjust, maybe could just have different sizes loops you could luggage tag on.