Here's what I had to do on my '04 when I replaced the OEM grille with the Bentley style grille as the OEM license plate holder would not fit. My first assumption is the holes for your license plate do NOT match up with the holes in the front fascia for mounting the plate holder. If I'm correct, go to any shop that deals in aluminum and have them cut a sheet of aluminum to the correct size (6" x 12"). I got mine off eBay. HERE'S AN EXAMPLE
Anyway, I then ground down all 4 corners to match the curves on the corner of the license plates. Then drill 2 holes to match where it needs to mount to the bumper. Then drill 2 holes to match the holes in the license plate. If there is a curve where it will mount like I had to contend with, I purchased a couple of nylon spacers at the hardware store to put behind the aluminum piece. The screw/bolt you will use will go thru the center of the spacer and all will be good. Just get the correct size spacer. I believe they are sold in various sizes in increments of 1/8"
The final problem is getting the license plate screwed into the aluminum since you won't have those built in nuts. I used a pair of metal clips like the one below. These are for a # 8 screw and were purchased in a bag of 13 at NAPA. The length from where it will slip over the top of the aluminum piece to the screw hole is just perfect. The flat side goes toward the front (facing the license plate) and the curved side toward the rear (facing the bumper).
The 2 white pieces you see in this image are the nylon spacers I mention. Just to the inside of each of them are the clips. Look carefully and you can see them slightly. The 2nd pic below is what they look like. BTW, all license plate frames (not holders) have their screw holes matched to the plates so you can install any frame you would like, as well.[ img ][ img ]