This is easiest to do with a friend in a private game, trading wins.
From the multiplayer menu, select jam session, and then create a new game. Select Monte Carlo as the location. Any track will do. Once the game is created, invite your friend into your lobby. Now start the race, and take turns winning. This should only take a few minutes total.
Find others to boost with here:
http://www.xbox360achievements.org/forum/showthread.php?t=31...If you do not want to do this with a friend, you will have to find a race in Monte Carlo, using the custom match selection in jam session. If you find a game, join it, and do your best to win a single race. If none are available you can test your luck at making your own lobby.