If you have a gps with one of those belt clips similar to the cell phone ones, you can do this mounting in 15 minutes. It will be helpful to grind down the sides of the belt clip so that they fit between ridges on the stem for the bolts. Then use one zip tie to around the the fat tube portion of the stem. Another zip tie goes over the tube, then over the bars and then back around again. This ensures that it won't shift in place. You could add another ziptie going the opposite direction just to be sure.
Then find yourself a piece of foam rubber for cushion and a small bungee cord to hold everything in place and voila!