Has it honestly not twigged or are you being mischievous? You'd moor on towpath side, wind the bridge up a bit (so the car is blocked, but you can get back to the boat), then ask the motorist to wind it up (make sure you're on the correct side - so you can get back to the boat!), you drive the boat though, then get the motorist to wind it down again. Of course, it would only work if the motorist was approaching from the side of the mechanism, otherwise there is no incentive for them to stop and help you.
Ha ha ha oh you little tinker ...... So I clamber out of the cut because I always fall in, I get the motorist to do the deed ... He then he launches the windlass back to me, which causes me severe head wound AND I end up in the cut yet again ..... Some plan man x
Oh Dog House where has your humility gone ? Grandad x