There are a couple of Arma 2 mods that essentially address this by checking to see if the AI line of sight is obstructed and facing the AI until they have an unobstructed line of sight, so hopefully this wouldn't a big time sink to fix.
Having the AI make subtle facing movements over time, changing their position slightly, would be a really nice extra- when there is more than one tactically relevant direction to face in. Otherwise it's really predictable to deal with AI in buildings, but that's just an extra wish.