I think if I just couldn't live with it the way it is anymore, I'd try sanding/shaving/filing the hole itself on the plastic ring. You could use a straight edge to mark a line from corner to corner, remove the ring, and gently (!!!) remove material up to the line. The hole would end up with a curved side and look odd of course, but it would hopefully appear correct once it was back on the guitar.
Another option is to try different sets of rings, (or dark ones where it wouldn't be so obvious). There's bound to be some slight differences in molded plastic parts, and you may find one that's just slightly smaller enough to work.
I think I could live with it the way it is, but I understand someone wanting things just so. Good luck with it whatever you decide to do.
Goldtop