The lens material is brittle!!! I have been able to heat it with a heat gun to mold it and used a Dremel tool to cut and trim it to fit. You need to use low RPM's while cutting it because if the blade turns too fast it will melt the plastic and fuse it back together once you make the cut.
Make a template out of paper or cardboard first then transfer it to the plastic you want to cut leaving room for error. Trim until youre satisfied with the fit.
Good luck.