You can convert a BSP into a static mesh in the Details window. It is under Brush Settings’ advanced options. Then from the content browser you can export the mesh created as an FBX. I hope this helps!
It works but there is a bug, the static mesh will have it’s Light Map Resolution set to 0 and has to be changed manually otherwise the texture says “INVALID LIGHTMAP SETTINGS”.
Actually it seems the Default for Light Map Resolution is set to 0 globally for the editor, as seen here http://puu.sh/89RjE.png
The lightmap issue is a known bug with converting BSPs to static meshes. We are working on a solution for that. Did this help you with getting the meshes you wanted?