Kyle?s idea is quick and easy and nobody would be the wiser.
If you truly want a patch, not easy but if done correctly can look good and purposeful, can be painted etc... AC 43.13-1b page 4-32 shows acceptable practices for patches. I would use that as a guide for rivet type and spacing and for a general idea. A flush patch can be made to look nice. You see them all the time on certified aircraft, access covers, even your wing inspection holes.
I would still use the mounting holes per plans so it could be converted later, as Kyle suggested. It will also look cleaner I think.
The biggest challenge is this is not a flat patch and most folks don?t have tooling to form a joggle (you can rivet a flange on instead). Matching the leading edge curve for the patch will require some skill. There are several ways to do it, but Kyles idea using the preformed lens is sounding really good.