If you had a manual pull on right click, and a release/start reload on left click, I think it could work with the current physics. As an estimate, give it 10 seconds of pull total per shot, in 5 second max intervals (so two pulls per shot if held). On each pull, the physics reset. Harpoon breaks after 30 seconds. Give it a short reload of 4 seconds. This is because it does not start reloading until you break the rope.
You could leave the harpoon attached, and just give a little pull once in a while for disruption. Or you could break the harpoon right away and start your reload if you are going for damage.