I vote for this method.Personally, I use 3M VHB "Red" double-sided tape. It's neat, there are no mounts, frames, screws, etc, and once it's properly adhered, it's on for good. Well, at least until you have a spare 30min and some fishing line .
Get it on ebay: Genuine 3M VHB Tape Sheet Mounting Adhesive Double-sided tape 100mmx100mm | eBay
I have done this on my last two Regs and bumped into my old 2013 7P recently and the Euro plates are still struck strong.
Trick is to form the front plate to the shape of the holder before adhesion.
Back plate mount a length of Aluminium flat bar with countersunk bolts onto the car and stick onto that.