Continuously stream the GPS data (ideally at up to the full 10Hz it is capable of, but I could make do with lower rates for now) out of the XBee (to a remote base station). Ideally I would transmit the whole NMEA sentence, but lat/long, and perhaps elevation would be sufficient.
Pay another $13 USD and duplicate the GPS requirement. You are making your life crazy for the price of a half-decent lunch!
Ray