What's so hard abotu mounting a plate? Self tapping screw, and glue some aluminum flat bar behing the moutning surface if the FG is too thin to bite into.
Sorry man, I hope I'm not coming off as an asshole, but nothing says butcher, hack job, etc than a license plate dangling in a non-stock location, it just completely destroys the car for me for some reason. If you're happy with it, have fun and run with it. That's the most important part