Select "Driver DNA Lab", then choose "Celebrity Face Off". Defeat the indicated driver in all three of his challenges to unlock the corresponding car.

Audi 1.8T Quattro: Caballero
Dodge Viper SRT-10: Samuel Hubinette
Ford Mustang Fastback: Djibril Cisse
Ford Mustang GT '05: Smudo
Nissan Silvia S15 Spec-R: Phil Morrison
Nissan Skyline R32 GTS-t Type M: Tarzan Yamada
Toyota Corolla GT-S: Beau Yates