Micro mark has a hole punch device that might help you its a little pricey .However a very precise tool. You could also take small cuts with an Exacto, start off with cutting it square, then attacking the corners to make it octagon, finally slicing the little bit leftover until its rounded. On the one I did. I put them in the water, slid them in place, blotted them dry, then add a small amount of Epoxy to glass them over.