We tried in a boosting-session and it does not work in a private game - it has to be in public mode.
If you are alone, you need luck to get bad gamers.
If you have a boost-team of 4 people, create 2 clans of 2 people each.
Then go to "clan"-tab and hit "play with clan".
Choose "Domination"-gamemode and make sure the option "Clan" is active and not public or privat.
Finally hit "search" together (count from 3 to 1 in party-chat).
Now you can bet for 99,99% that you come in one game together, because there are not much clans active and the active clans must be searching at the same time as you and must search at domination to get into your game - and I doubt that will happen... :P
After the round, choose the map-vote and vote the next domination-map so all people in the session can get the trophy.
I hope this guide helps you guys. 8-)