Are you calling for creativity? How about this autoadjustable system... Just the jibsheet (yellow) but attached differently, and with a different kind of block (violet).
The "equivalent" block position would be somewhere on the imaginary line between the violet block and the yellow sheet end, and would move forward as back in the way that it is supposed to, wouldn´t it?
It would be slightly less than 2:1, but not too bad.