I'm embarking on finishing part of my basement. Essentially, we're talking about finishing two rooms. I figure I need two or three six-inch heat runs per room and a cold air return in each room.

The complicating factor is the stairs that run parallel to the main, between the two areas. This stairway apparently forced the HVAC guys to install all of the runs for the main floor of the house at either end of the main. Now, there's no "open section" of the main, with access to the rooms, where I can start my new runs for the basement.

What are my options? I already know that splitting an upstairs run is not a good idea.