This topic is of great interest to me, I'll be back to the boat in a couple of weeks and will be straight into the rigging and sailmaking. I had not thought about the halyard twist problem, and I think I may increase the drift a little at the expense of some sail area.
The way I used to sail my old gaff cutter was to rarely ever touch the sheet to tiller steering, I could put in the first two reefs without altering anything and reefing the main had little affect on the course, because the steering sail was still shadowed. However the reefing process involved a lot of deck work which I would like to eliminate, and I'm hoping to keep sailing the same way with the junk rig.
Something I learned about gaffers was that the lee topping lift is your best friend when reefing off the wind. I would literally drop the throat halyard, the momentum of the gaff would carry it well down the mast, and the peak would swing well forward and down, slacking the leech. Most of the wind force would then be taken by the topping lift, and it was pretty easy to haul the leech down. After I put plenty of baggy wrinkle on the topping lifts it was even easier because almost all the resistance was due to friction.
I'm guessing at this point, but I think something similar should happen to a junk sail when you slack the halyard and/or throat hauling parrel? I would think that minimizing all areas of friction, especially the topping lift, possibly sewing patches of something slippery on the sails where they will contact the mast or topping lifts, would help make it do-able.
What about grabbing the sheet and shaking it vigorously (from the cockpit, of course)?