Lon,
Sorry I am not quite sure exactly the situation you require this to work in.
You say you want it to pass through Wall/Floor then in the next sentence suggest you dont want it to fall through the floor.
Anyway I am sure you can do what you want via a combination of static/dynamic - objects/entities and script combinations calling collision on or off when appropriate. You may have to use a trigger or something of that nature to switch on or off the collision or "activate" an entity at a particular time of collision or proximity of another if thats appropriate....Something along the lines of that kind of thinking anyway.
A couple of objects in a test level together with some messing with scripts should sort it. It can be frustrating I know trying to get some of these things to work but most things of this nature have a solution in FPSC with enough trial and error workarounds can usually be found.