Mainsail sheeting design without a track.

the original pix are of a double lead mainsheet. while it is not intuitive, moving the traveller car on the inside purchases does change the direction of the pull, in spite of the outside falls going to fixed positions.

contemplating some kind of dual mainsheet system would be unsafe as previously noted. you can vang sheet as suggested to obtain less twist provided you have a powerful vang and boom, however it does not address the issue of allowing close sheeting without closing the leech, as you would like in light airs, and would normally achieve by setting your traveller to weather.

however you may wish to use an adjustable bridle to solve this problem. if you like the look of the original pics you can just do that only with the center block going to a bridle bridle pic make the legs of the bridle adjustable and you'll have your control but still be able to let the mainsheet run in a puff.

 

I had a horse on my first boat for the trip from BC to New Zealand . Noisy as hell in a calm . Threw it overboard in New Zealand and went for padeyes; much better. A track would have been just as noisy. On cruising boat you can always vang the twist out , something you have plenty of time for. I leave a 6 ft by 1/2 inch line around my boom . When I ease it out a bit , I tie this to my cabintop handrail and ease the mainsheet off completely, Further out, I tie it t o the rail and ease the main off. All the way out ,I tie it to my chainplates, then pull the mainsheet in , flattening the main, until it is clear of the shrouds. I haven't felt the need for a track in 35 years.
Brent

 

Mainsail track.

If you have an adjustable boom vang, there is less of a need for a track.