Nice try [:)]
But I think there's an easier way to get the counter-top you wish using an elevated room, because a texture along the thickness of a room is applied the same way it is on an object (i.e. it's nice on the front face). If you import an invisible box as a staircase, place it at the lower level and make it higher than the upper level, this will create a hole in the upper room for the sink. Then, you just have to export to OBJ format the room + the invisible box to get an importable counter-top.
Please see attached file.