What if it were the actual stack itself? In my kitchen, the stack (which has a tub, sink and toilet feeding into it in the bathroom above), runs on the outside of the 2x6 wall. I was thinking of adding an offset of about the size of the stack (so 3", with 2x45's at the top and 2x45's at the bottom), just to recess it behind the wall. This would avoid having one of those unsightly "boxes" in the middle of the countertop. I would only offset it for the distance between the upper and lower cabinets - I don't mind losing the space in the cabinets.