Chris:
If you intend on attaching sides - I normally attach 1 inch 3/16 thick hardboard with super glue - the bow will disappear. If you are making a row of fronts simply cut an OGR blank wall into the strips for the two ends of the row (I use Plastruct Plastic Weld).
If not try Melgar's method - just make sure as Melgar says to clamp and leave over night and make sure the wood is thick enough so it stays straight and does not conform to the bow in the wall.
I just read an article in an old Model RR magazine in which the author wanted to deliberately curve a Magnuson wall (not sure if it is the same kind of plastic as OGR). He did so by placing the wall in a pot of hot water - just short of boiling and forming by hand. You can try the opposite by placing the part of the OGR wall with the bow in the water then put it on a flat surface and place a brick or barbell weight on top of it.
Joe
