MMS Backfill - Settings Request ("Fix")

The current options between Island Settings & the Round Settings Device don’t allow for what seems to be the most obvious need.

Scenario:
A 4-player game with a custom in-game pregame system, MMS Backfill is enabled by default to allow the game to fill up.

After this custom pregame, I’d like to disable MMS Backfill while still allowing Social Joining.

After a game is won, I’d like to re-enable MMS Backfill to allow new players to fill the lobby.

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I have attempted to use multiple Round Settings Devices that get enabled/disabled, but there is no way to always allow Social Joining whilst having control over MMS Backfill based on the gamestate.