This is easily boosted, or very easy legit if you have a friend and use party chat.
The achievement will not unlock if you aren't winning against another team.
In this mode, the driver can't see checkpoints and is directed by their partner via the dpad, or to make it easy, party chat.
It can also be easily boosted with four players.
I'd recommend choosing Arms Race (under the normal race mode) then change the settings to rally mode.
Then just let your partner direct you, or learn the track then start again and invite a load of randoms. Me and a friend did it this way, and we won by a million miles, as the randoms aren't in party chat.