Here is an idea on how to create a game controller that lets you move your device in two planes using just one hand. It works well with apps that use a gyro to measure tilt. Feel free to change and adapt parts depending on what you have available. You can probably improve on this idea and customize it to suit your needs. Adding motors to control it could be interesting.
These instructions are shown in two parts. First shown is the cradle. The XY controller is shown later.
This is the controller part. Use your favorite size tire for the grip. The part shown below will fit into the module shown above, snapping in at the center pivot point (the two little grey studs shown above on the two black top cross beams).