Like a lot of people, I have a server I don't use for much other than lobbies and scrims.
I'm sure this suggestion will shock and awe some people, but there's really no reason to ever NOT have a badwater/viaduct/etc. lobby running, and if there was an option like "run this lobby until I disable it," I'd use it.
The only wrinkle I foresee is needing to exec a "lobby_off" or explicitly restart (rcon quit) the server on each iteration.