Walls for organic rooms

It seems that Organic Rooms is the only way to have a room which doesn't overlay a floor on terrain. What if we could create a "room" which in fact is a outdoor room but have walls and gates for example. This would be nice when creating a small fortress map. Right now, afaik a Regular Room will always generate a floor. When editing, it's is possible to toggle off floor, but regenerating will take no effect.