If it was me I would:

1. Make sure I had a bot in the room 24/7
2. Use this:
Code:
ON *:BAN:#: {
  if ($ibl(#RoomName,90) != $null) {
    mode #RoomName -bbbbb $ibl(#RoomName,10) $ibl(#RoomName,9) $ibl(#RoomName,8) $ibl(#RoomName,7) $ibl(#RoomName,6)
    mode #RoomName -bbbbb $ibl(#RoomName,5) $ibl(#RoomName,4) $ibl(#RoomName,3) $ibl(#RoomName,2) $ibl(#RoomName,1)
  }
}
This would unban the first 10 when your room gets the 90th ban. Giving you a theoretical breathing space of 20 lusers.

Tested and works.