I don't know if this is historically appropriate, but from a gamer's perspective I think there should be a "Reverse" command to move a brigade backwards to a given point in an orderly fashion while still facing the enemy.
Right now, there's only "Fallback", in which case you don't really control the direction of the fallback, and a normal "March" or "Run" command, where your troops turn their backs to the enemy, when marching back towards your own lines, getting a "Flanked" or "Rear Flanked" malus.
Just give it a command like "Shift+RClick" or something like this.