It's not glamorous, but there's always the brute-force method of just creating two videos, one for each side. I had to do it once for a three-projector wide stage performance.
In After Effects, I set up my composition to be three times wider than normal, then produced the video in that. I then nested that comp into another comp with the normal resolution, but three times. Then I rendered the video out three times, one for left, one for middle, and one for right.
Like I said, it's not glamorous, but it would get you the results. Someone else may have advice on how to do it within XPression.
#XPression