1. Put the [MvM-D] tag on while you're playing a game to make it apparent to any randoms that come along that you're in a group, especially if you're not searching with a full lobby.
2. Try not to kick a random for merely not complying with your special restrictions. For the most part, members of this group are very high tour and could conceivably solo Oil Spill. Not everybody will want to play the way you do. Explain to them what you're trying to do and invite them to play along, but let them do their thing. By all means though, kick asshats that are ruining the game for you by saying abusive things, purposely playing poorly, griefing, or generally raining on your parade.
3. Try to lobby with a minimum of 4 players. This will keep you from being voted off for breaking the meta with randoms.
4. If your game isn't working out, consider loosening your restrictions. We want to have fun and kill bots in new and inventive ways. If 3-man pistol scouts on mannslaughter just isn't getting the job done, then don't handcuff your team to a losing idea.
5. If you're going to go with a short roster, invite any randoms to watch but not interfere. If they comply, they keep you from having to explain yourself to new randoms. Put on the [MvM-D] tag so it's apparent you're all together and trying to do something different. If they interfere, feel free to kick them. If they're finishing a tour and they get a free aussie ... well, take a screencap and post it here so we can all engage in schadenfreude.