I avoided drilling an additional hole by running the camera wire through the existing hole for the wires that power the adjustments and defrosting features of the side mirror. You do have to remove and re-install the mirror, so this may be more of a job than just drilling a hole, though.
I agree with DSDP Don that the side camera view should be independent of the rear view camera to maintain the image of your toad when passing. I have found that I don't rely on the side view camera much. Using the mirrors and the rear view camera works for me. However, having a second set of eyes in the passenger seat is the best viewing assistance that I've found!
Good luck with your project and maybe I'll see you down the road.