Converting complex BSP's to a static mesh?

I blocked out & textured my level with BSP’s and want to convert them to static meshes. When I go to convert my geometry, I am only able to export the room as a whole (floors, ceilings, walls - the room was built off of one hollowed-out brush). I would be fine with this, except it has other pieces of geometry (such as the octagonal rooms) which is making it a pain to add collisions. Is there a way to convert certain faces from a BSP to static meshes (or maybe recommend another way of converting my geometry)?