Hey Will. I was in the same position as you, want to use synthetic line but can't be switching back and forth between one for plowing and one for winching use. But I also didn't want to chew up my nice synthetic line. So here's what I've done and its worked well through 2 winters.
1) ditch the hawse fairlead. I started with a brand new standard roller fairlead and all been good so far with that
2) use the sleeve and stitch it in place, one stitch at the end of both the rope and sleeve, and one at the other end of the sleeve wherever that ends up on the rope when straightened. I stitch the end of both together first, going through both rope and sleeve a few times using 6 lb test fishing line. The I pull the rope tight and affix it to something, then pull the sleeve tight and then let the sleeve back about an inch and stitch that end in place there. I don't ever winch around rocks or trees so I can get by this way. If I did I would just add a second sleeve and keep it wrapped at the halfway point on the rope and let it slide for rocks and trees.
3) I've got a couple setups that have been using this. One with Amsteel blue I bought from Midwest Winch Rope website and the other with Sedeta (Dyneema) I got from Amazon. https://www.amazon.com/Sedeta-Durabl.../dp/B013B348IW
3/16" for both. In the future I'll buy from Amazon, seems just as good and the price is right.
4) I figured this solution out not from winching/plowing, but from 3 years ago when I came up with my own wheelchair loading mechanism for my wheelchair. I used a winch and synthetic rope and there was one part where the rope had to slide over an edge. So I did the sleeve thing and I use it 2 to 6 times a day, every day now for 3 years. So when I then got into plowing, I knew this would do the trick. So far so good.
5) I buy my sleeving (tubular webbing) here: https://www.rei.com/product/107605/c...ubular-webbing