There are aftermarket tombstone taillights that will mount to a flat/smooth fender. I have one hanging in the shed I never used. It was a Drag Specialties or CCI part number.
Yes you can do it.
I mounted a JP cycles tombstone to a Klock Werks fender. I had to drill 3-holes, 2- to mount the light, and 1- hole for the wires to pass through. It fits the shape of the fender just fine. If I remember the light was from Custom Chrome, around 40 bucks from JP.