The G-Tech comes with a swiveling plastic pad that is flat on one side and has suction cups on the other. They also give you some velcro. The idea is you velcro the G-Tech to the base and suction that to the windshield. This mounting contraption also has a hinge that lets you adjust it's angle.
You could, however, stick the tape to the top of your dash, or anywhere really. The GTech MUST be in a position where it can be adjusted to perfectly level, and on different roads, you WILL need to level it before you use it. If you stick it to something permanently, make sure you can adjust it's pitch or else you won't get good readings.