What about a system that detached the crossbar from the rudders?, at least on one end... maybe not perfect, but would probably result in the boat sailing out of control / tipping over... Just a random crazy thought.

I would think a system that is an extension of the mainsheet / traveller would work best, sheeting in the system once you are say 10 or so feet back (maybe 20 to get out of wash) making the boat tip / keep you connected to the boat. I've done enough offshore stuff to know that the tether is a great idea, but you ALWAYS want a knife with you if using one just incase you need to cut it (most of the time the tether will try and drown you, especially if too short). Their are knifes specifically for this that are easy to use and made to avoid cutting yourself.

My 2 cents