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Step 1: Get you and 2 people in a lobby
Step 2: Invite your friend(F1)
Step 3: Have another friend(F2) get ready to join your lobby
Step 4: When your friend(F1) is at 70% loading, kick him
Step 5: Once you kick your friend(F1), friend(F2) needs to join your game right away.
Step 6: If you did this right, you should have at total of 5 people in your lobby.
Step 7: Make one of your friends (that was in the lobby at Step 1), leader of the group and then leave the group
Step 8: Join friend(F1)'s game
Step 9: Now there should be 5 people in your game and only 2 of you in a group.
Step 10: Rinse and Repeat once you get the desired amount of people
Step 11: Start a mission and have fun