Okay, this is implemented in 937911633a3523fbbc5817f9c476c3f3a9823bd0.

It was somewhat [sketchily done](https://github.com/mozilla/zamboni/pull/1071/files#L1R28), but it works, and [is tested](https://github.com/mozilla/zamboni/pull/1071/files#L3R592). Feedback, anyone?