Step 2: Begin!
First, attach the GPS to the belt clip, and then place the belt clip on top of the handlebar area. Move it around a bit until you find a position of the GPS that you like. Remember that spot.
I don't really know how to say this well...
Tighten one zip tie below the leaf spring of the belt clip, and another above(see pictures). This will secure the belt clip to the handlebar and keep it from moving up or down. You could also just use epoxy, but I wanted the belt clip to be removable. I would not clip the zip tie ends for now, as you may decide to reposittion the clip.
Don't worry about the big gap between the bottom of the GPS and the handlebar piece. We'll get to that.