I don't know if there is an automated way to pan the audio, but you could try this manual procedure:
1. Copy the audio to another track (you may want to split the video and audio tracks temporarily in order to avoid copying the video as well).
2. Make sure the two audio tracks are in sync with each other (and with the video track).
3. Set the balance of the tracks to left and right respectivily.
4. Fade out one track and fade in the other track around the position where you want the panning to occur.