Some states don't require a front plate, but if you have to have it, MB supplies a bracket. Shockingly it is meant to screw right into the painted part of the bumper cover, just below the star. If our dealer hadn't done this already, I would have explored alternatives, like the double-sided tape that the spoiler is attached with. Since we have holes already, too late for that.
The next issue is that the bracket curves to correspond with the shape of the car, so a plate needs a slight bend to follow that curve. The bracket is marked for four screw holes, useful for keeping the curved shape. The top two holes are right in front of the same painted section of the bumper, so I didn't want to drive big screws into the bracket and damage the bumper further. The bracket plastic is not very thick either, so I wanted more depth for screw threads to grip.
So I went to the auto parts store and got some ordinary square plastic inserts, packaged with long screws. I removed the bracket (two screws and a plastic clip that goes into the lower grille). I used a utility knife to cut recesses for the plastic inserts. I used a hacksaw to cut the long screws shorter, so they didn't protrude any deeper than the rear of the insert. Then I remounted the bracket, attached the plate and put some screw covers over the screws. These are OK, I might look for better ones.
I was looking forward to taking off the tacky dealer-supplied front decoration:
The bracket with three plastic inserts installed:
A closeup of the insert flipped over, and the hole I made. It doesn't need to be this complicated:
The finished plate. I wanted a minimal installation: