Two ideas for your problems that MAY! help ?
In the past it was not unheard of to have the last block before your hands to be on the boom and a block and cleat fitting is on the
http://www.Harkenstore.com website.
Big Bullet Blocks
Item, 140 or 141
Would free the cockpit somewhat!
The other mainsheet I have seen fitted to a boat was started on the strop at the transom, led to the boom outer end block,along the inside of the boom to the gooseneck.
Turned via a block down to the floor or heel of the mast then along the side of the centreboard box and then up to a centremain jammer that was adapted to have the sheet enter the jammer from below.This was set to one side of the centreboard box.
Makes a hole below the waterline otherwise ? 😉
This worked very well on a racing Albacore at the Worlds and the cockpit was very free to move up and down in.
May help !!
C P 🙂