For those who want to do this in the career mode. As soon as you unlock Ken Block Ford Focus 1-On-1 (Seeker Championship), choose Unbeatable difficulty and turn rewind on.
You will start on a straight and instead of braking at the end of it, just slam into the back of Ken Block. If you hit him well, you can push him into the off-shoot on the right and he will lose heaps of time trying to join back on the track. If he manages to get close to you, all you have to do is block him (race is only 2 laps).