If you go to a BMW dealer, they will sell you the GPS mounting bolts from an R1200GS. They are the correct size and pitch to replace the stock KTM (and most others) handlebar pinch bolts. The BMW bolts have an extended top that is threaded so you can bolt a mount right on. I took a Touratech mount for my 60 CSX, drilled holes in the back to match and bolted it right onto the BMW bolts. If you have a horizontal format GPS, use the BMW bolts on the left and right pinch bolts, then connect the two with a piece of aluminum and use that to mount your GPS. I have a basic pic at home, can post after work. I don't have part numbers, sorry.
Edit: Pic as promised