An easy way to do this is to host a game and wait until you have at least 6 people present. If i were you i would wait for more than that because some people can't always stay and finish the game. Once you have a good party size simply stack all the good guys onto your team.
Keep in mind however that some of the people on the other team may leave because of this. (another reason to have more than 6) You should also try to keep the teams as even as possible to prevent people leaving as well.