You have to pass all the other champions and when you reach him, I think you should get a lot of the speeds(green block) and get 3 whites. Try to get as many as him and you might win Rocket Racer. (You might be lucky enough!)
theres a glitch in the game so that if you do the race and make yourself mess up alot you can play it again and ether he will do the same thing you did or it will be easier