Either grab a partner and play until you win 20 games, or fight Kinect's recognition software and go solo.
For solo play, choose your profile as the blue team. For the red team and choose to correct your identity to a dummy profile on your system. You will have to fight the recognition software and correct your identity repeatedly, but by controlling the red team, you can make them receive three immediate strikes, making the process a bit less tedious. Once they've received three strikes, the team is disqualified, and you can finish the game as the blue team without having to fight the Kinect.