As andy had said i shouldn't post if im unsure of the answer, but to try it never hurts...I know its not EXACTLY your match of what you want, but is it possible to put a trigger_multiple where they go the most, and least likely for an assassian to go...I don't map for TFC since i hardly play it anymore due to lack of connection speeds w/ satellite...But if i did this for Half-life, which is pretty much the same engine, i'd make a trigger_multiple(or once, or relay. your map, your choice)
I'ma shut up before things get ugly