What about a Hid-a-hitch? I saw...years ago a hitch that will mount behind a roll pan and come out directly behind the license plate. The plate would fold done on a spring loaded set up for when the ball is installed.
Doing this may be an option
That is RIDICULOUSLY easy to do! I did one on my S-10 Blazer I used to have.
I took my plate off the rear, taped over where the plate would go with masking tape, then put the plate back on. Doing it this way, I was able to trace the outline of the plate on the tape, and not on the painted surface of the roll pan.
I carefully measured where the receiver hitch would be located, then cut (2) 4" holes side by side from the center, and cut the "V" from the top and bottom. I ended up with an oval 4" high by 8" wide.
Then, I scrounged around in the junkyards, finally found a flip-down license plate holder from an early-80's Cutlass Supreme (any car with the gas filler behind the plate would do). I mounted the bracket upside-down, covering the hole in the rollpan. Bolted the license plate to the bracket, worked flawlessly. Whenever I needed to use the hitch, I'd flip up the plate, and the oval hole would allow me to slip the pin in without having to crawl underneath the truck.
I also had the wiring harness attached to the hitch mount with a bungee cord - completely stealth.
