With some geometry, you can figure out your orientation and acceleration in any given direction. The 1.0G will always be there, though the direction may change. The Accelerometer will give you a vector that is a sum of the acceleration of your doohickey + gravity. It will help immensely if you can maintain a relatively steady Z so you have an easier point of reference, or if your accelerations are not constant, then you can use previous readings to measure current readings to determine orientation.
You do make it difficult if you can't assume down is down.