I got no farther than you have in that I have thought about it. But I can't say that I have even looked up under that part of the rear bumper. I did feel up under there. There is quite a lot of "milk crate" cross-bracing in the plastic. They way my mind works is that I think about something and while asleep the way to do it usually comes to me. So what my mind told me to do was get some PVC pipe of the size I wanted to make the hole in my bumper. strap it down to something at the height I wanted to make the hole, then cut the end of the pipe until it was the shape of the curvature of the rear bumper at that point. Then all you have to do is outline the pipe shape on the bumper at the two locations you want to make the holes and cut them out.
I was thinking of only going up half way of the tips, or cutting out a half moon shape in the lower bumper area in two locations. Then you could use some chrome push on door edge trim around the cut to dress it up. The original concept Nitro had recessed tips like this.
After feeling all the plastic bracing under there, I kind of decided to leave well enough alone. But if you can make this work, kudos to you and I would like to see result.