Changing the rear number-plate holder last update: 21 November 2009
1. Move the fog- and reverselights
2. remove screws "1" (there are four)  Don't touch "2"
3. remove the number-plate lights and cut away the upper part 
4. Install a standard number-plate holder with two stainless steel angles
5. Install one of the number-plate lights.  I did it with a piece of aluminum sheet metal.
.... et voilà 
for comparison