Holy thread resurrection batman.
The only practical way to implement this would be to allow lobby leaders to ban spectators within their lobby.
I have talked to the dev team about this before, and it wasn't something they were interested in spending time developing. Wether because they dont agree with the principle, or it would take too much work and redesigning to be worth it, I dont know. But it is very unlikely anything like that will be implemented.
Also this is marked approved because the original thread was asking for lobby leader tools, which you now have.