I was faced with a similar situation with an Ameritowne building. I have one that was finished on 3 sides, but had a plain/unfinished back... which worked fine, until I needed to relocate the building to the middle of the layout where the back would be visible. I tried using a different brick pattern on the back, but it just didn't look right.
In order to match the existing brickwork color/texture I took a picture of one of the finished sides, cropped and scaled it to match (which took a couple trial runs - including getting the lighting right on the photo), then printed it on a high quality printer. From there I just glued the paper in place, then added a fire escape over top of that to sell the effect. From more than a foot away you can't tell that the brick is just paper. If I can snap a pic later I will post it.
-Dustin
Edit: Added pics of the "take a picture of another wall and glue it" solution for adding brickwork to a blank wall. Not perfect... but not too shabby either:
