Possible approach to that would be: copy the portion of the model to the side a specified distance clear of other work. Erase what you do not want, make the remainder a group or component. Then, set this back in place and raise it a small increment, and shift it so that it is "parallel" to all. However, if this work curves in on itself, you would have to maybe scale it down a small amount so that it is concentric at all points, sort of like the way Offset automatically resizes to fit. You gave a stair example. If it is stairs, it is important that the treads and risers be consistent in dimensions all along the flight.