Last time I heard this being bounced around, the consensus seemed to be that the best jerry-rig would be to use a spinnaker or whisker pole with some large u-bolts (kept for that purpose) to affix a door or table (pre-drilled) to the end of the pole, and then using that "steering board" deployed from the stern, so the board was as far aft of the boat as possible in order to get more leverage against the pivoting on the keel.
Maybe that's what the concensus was, but there was at least one case - reported here on Sailnet even - where the crew spent valuable and fruitless time trying to rig a jury rudder only to lose that too!
One has to remember that, in the sea conditions where this is most likely to happen, the crew will also be exhausted from getting bashed around and possibly even have other things to worry about (like water coming in, for example). Wasting valuable time then putting together something that doesn't work on "your boat" might cost your your life in the end.
If you're doing a long trip and worried about Mutiny By Rudder, the best option is to fit one of those fold-up "emergency rudder" thingys on the stern that can be easily deployed, even when exhausted, and actually work... (sorry, no time to find a link now)
Apparently a lot depends on the hull shape and stability and balance, or lack thereof. A boat that balances well and steers well under just sail trim (with no rudder effort) should do better than one which always needs some rudder. But I don't think I know anyone who would be willing to drop their rudder and then go out for practice.[g]
True, however one advantage of a trailable yacht is that the rudder usually folds up out of the water - as if you never had one. It's a good place to learn if you've never tried... and the application to increased boat-speed when you go back to the helm is priceless.