the easiest way to get this is to set up a short private race with a friend or boosting partner. top gear west set on 1 lap is probably the quickest way just get your partner to follow behind and cross the finish line as close to you as they possibly can.
you can also do it the other way and actually win multiplayer races and hope someone is close enough to you for this to unlock but unless your really good you will find it frustrating to use this method