I never liked the way the license-plate mounts to the GS- to me it looked like a factory-bodge of the mount for the big square German plate, and I didn't like how that big bit of black plastic hung down so far from the tail- rather ungraceful-looking (but still not as bad as the similar bits of a V-Strom!

).
So I did a little surgery, and this is the result:
Looks much neater and cleaner and less obtrusive. So how did I do it?
1) I took a hacksaw to the plastic-bit that hangs down from the tail.
2) I removed the rectangular reflector that lives just below the tail light.
3) I trimmed the plastic bit where the reflector used to live, paring it down a bit but leaving most of it intact for structural reasons (since one of the light-assembly mounting-points in on this bit).
4) I used cut some aluminum flat-stock (1.5" wide x 1/16" thick, available at Lowe's or Home Depot) into two 5" long pieces, then drilled three holes in each. Holes were placed after doing some measuring and sketching.
5) I trimmed and rounded some of the corners on the aluminum to prevent protrusion.
6) The top-holes in the aluminum pieces go around the two upper mounting-studs for the tail light. The pieces hang down.
7) A little bit of spacing is required to get the plane of the plate to clear the bit of plastic where the reflector used to live, so the plate is spaced at the two top screws with a pair of washers and at the bottom two screws with the bit of plastic where my state's safety-inspection sticker lives.
Here's a view of the assembled bits:
As you can see, I left the amputation-area a bit rough...I was pressed for time that day. But I will do some careful trimming to improve the appearance, and fill in the holes left by the amputation. I really wasn't very concerned about moisture splashing up into the holes though, as if you have ever removed the tail light you know just how unprotected the wiring to it is from the elements. This decision was vindicated several days later when I rode through a lot of rain and had no problems with the light.
Also two days before that I rode through some very rough conditions on some unpaved mountain 'roads' (some of which were bad jeep-trails or even goat-trails!) in OKlahoma, and nothing came loose. The beauty of this mod, and the secret to it holding up to so much abuse, is the simplicity of it- just two bits of aluminum with three holes drilled in each, secured to the bike by existing fasteners for another part.