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.
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]