oh, sorry...I didn't mean to imply that one would want to use per-frame terrains, I was referring to the obj objects etc...
one way to get terrains with overhangs into LW (or whatever) would be to use the LW exporter from a series of cameras placed to get as much of the terrain as possible - then fuse them, then hunt down any little areas that have low detail etc, and fix them with the standard poly tools...