Here is a discussion OrientationSensor Pitch movement (or how to use Accelerometer to detect movement) .
I think there is an example (incomplete) using an accelerometer to detect orientation/movement. There is an example of using a gyroscope sensor at the end of the thread. If your device has a gyroscope, you might use that.
If all this fails, you could make a 'joystick' out of buttons to move your Sprite, 