OK I know everyone says if you want certain people to join your game then make a private game. Honestly that sounds good and all, but it's not very practical for people who don't like trolling the call out forums.
My suggestion is would it be possible to create games where you can save a spot for your teammates?...
Create a game and have the option to add players name to your team under the how many players selection.
OK now instead of having -empty- slots you would see -reserved- and others could join in unreserved spots!!! This would be a great option for clans looking to practice certain maps without having to be online or spending a lot of time and energy trying to organize private games...
The reserved would be resolved by your suggestion Andy, however just say I see a 3 player game i'd like to join - I have no chance of getting my team in unless they are all online at the same time and even then you sometimes get a random getting in as the team is joining.
It would be useful to have some kind of unique identifier that allowed you to reserve the slots for other team members. Reserve slots could expire after 12 hours.