It would seem to me you could lash together two S7's with a single controller if you were to lay the miners on their sides, so that the "Top Side" were facing each other. Kind of awkward to wire up, but it shouldn't take any "long cables" to accomplish.

It would be interesting to know if the S7 cooling actually requires that the blades be vertical to work OK. While it's obvious what the "expected" orientation is, does it still behave well if it's laid on it's side?