That wouldn't address the problem in this ticket or Mythos' suggestion, it would only be a minor visual enhancement. Wraitii is correct that it has never been implemented since the simulation rewrite. Building placement is buggy all around, walls are maybe the worse case, because they need to reach otherwise impassable terrain to seal it off (not only cliffs but shorelines). And there's a ticket for it, so we only need someone to work on that http://trac.wildfiregames.com/ticket/1610