I have not opened the tunnel to see just how everything is situated, but it seems the two smaller pipes could be placed one on top of the other vertically. Basically in the same position as the existing one but stacked. This would be about the same height as the larger pipe diameter. Being a "heater" supply, there would be no real down-fall with the two running next to each other, like say the AC hoses where the heat exchange might decrease cooling performance. Naturally the shapes of them would require some changes, which would be easy to do if replacing the tubes with newly fabricated pieces. But I'm just speculating. If I wind up opening the tunnel on mine I will look into relocating both heater tubes in there, in an attempt to remove all heat sources from the interior space (i.e. the spare tire well, etc). It also seems that would make for a much cleaner install with the heater hoses running parallel from under the car up to the engine; especially if the attachment from the water pump return tube was on the right end of the tube, near the one for the other hose. Again, just throwing out thoughts.