International cyber cup server has an example of how can it be done: they have 'team balance' fake mode, '-tb', as an addition to normal modes
With this mode it is impossible to manually change slots, they are autobalanced when game starts
But since on lagabuse it is possible to change current game mode anytime, also there are some !hcl technical limitations, it is quite a challenge to make 100% similar mechanic
Instead, this 'team balance' could be set before game starts, for example, by a new command, like '!pubt' (or something more semantically readable)
So this lobby will stay autobalanced, while normally '!pub'-ed games can be manually balanced
But it brings some kind of hell, since we already have pub-command separation, for two versions of map, so with my suggestion it would be solid four commands for players to remember.
Maybe it could be some argument to existing commands, like !pub tb SUBSCRIBE_TO_THE_DEER_RADIO_[GAME_NAME_HERE]