I have tried working on this a month or two back and I nearly accomplished it but scrapped it. I have finally done it...
INSTRUCTIONS IF YOU DON'T KNOW HOW TO GET THEM:
Press and hold down the "CTRL" key or button and press "W". That should take you to the Vehicle Customisation Menu. Look for a small tab called "Body".
Click the arrow next to it and it should expand the menu with more parts. Look for "Front Bumper" and "Tailgate".
Click the arrow next to those two tabs and you will see the front license plate on the "Front Bumper". Click "Front License Plate" and there will be two options. One of those is "Front EU License Plate". Click that and that's the front plate done.
Do the same as the front one. Click the arrow sitting next to Tailgate and you will see "Rear License Plate". Click that and choose "Rear EU License Plate". Then you are done.