You can find boosting partners here.
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 Rallycross, and then Shibuya for the location. Any track will do. In advanced options, select 1 lap. 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.
If you do not want to do this with a friend, you will have to find a race in Shibuya using the custom match selection in jam session, under rallycross. 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.