After scrapping the idea of using one side of a door hinge, I went to get a big flat washer as someone suggested. Filed the hole a little bigger and smoother and stuck the cable and grommet on through. Now I'm trying to imagine what kinds of problems I've set myself up for.

If I got the picture set up right, you can see sacrificial 13mm wrench #2 peeking through the hole there. The first little thin one actually broke in two from the pressure of the cable. (the wrench fits just about perfectly between those two bolts tightened down on it) The black panel was bending down from the top, so I had to brace something on this side of it.

I made a mark around where the washer should stay so the cable doesn't rub on the original hole. Drove it a few miles, and it shifted a little, but the cable still isn't rubbing. Maybe I don't really need to start drilling holes and things to fix it in place, maybe it will stay in place well enough ... ...