I hear you on learning new workflows- which is actually what I'm discussing here in this thread- the bounding Corridor Graphic is new in SS3. This graphic is also nice because its a 2D graphic and easy to grab, etc. Arbitrarily clipping a corridor is not what I'm after- having 1 corridor clip another is truly dynamic interaction at its best, so if the 2nd corridor modified, the clip on the 1st automatically updates, etc.
With that being said, your example does show me an example I had not thought of. Alas, current WAD works great for you, not so much for me. Atleast I have a manual workaround in that I can choose this non-triangulated dummy component as my clipping element- almost giving me the same result except that if I have multiple places (dummy components) along the 2nd corridor (that would be clipping the 1st), I would need to select multiple elements instead of a single corridor graphic.