Nice!
I was speaking to Franc about this at the Dragon earlier this month. I saw this on an ad:
No Holes License Plate Bracket - F10 5 Series 2011+. F07 5 Series GT - Turner Motorsport
$80 is a bit...pricy. Even for a BMW-targeted part. BUT, anyone with skills should be able to make one for themselves for ~ $20.
It uses the recovery hook for the mount. You just have to come up with a hook/screw to attach it. Go from there.
A small u-bolt to attach and build from there.
Just a thought.