You must earn 50K from other players using your Tune. You earn 100CR per download, 500CR per like, and 200CR per use. I highly recommend doing this with a friend and at the same time as these, which are the 300 laps in MP and 122 tracks played:
First, exchange a Tune and Design with your friend. Choose one of the fastest cars that you both own. My friend and I went with the Nissan GT-R Black Forza Edition. Playing the 122 tracks plus the download and like gets you 25K, which is exactly halfway there.
This leaves you with 125 more uses required.
On your own time, each of you go to Freeplay, and pick your car with your friends Tune and Design. Any track will do, I use the Test Track Airfield, and set it to:
Game Type - DRIFT
Max Drivatars - 0
On the Advanced Rules menu:
End Condition - All Players In Bucket
End-Of-Race-Timer - 0
The event will end immediately. Click Restart, then Start Race, rinse and repeat. It takes 20 seconds total. That's 3 events per minute. That's 42 minutes total for the 125 uses needed.
In summary, pair it with World Traveller and Devoted Racer, and with the Design too, then 42 minutes of boosting and you're done. Also, you won't have to hope that strangers download and use your stuff.