Instructions
Obtain the reward card required to unlock Cross' C6.R by earning the Iron Wall achievement. This card is earned by successfully completing 20 defensive races throughout your career. If you are at the start of your career, simply aim to complete as many defensive races as possible as you progress. However, if you are at the end of your career, you can go back to finish more.
Load your career profile from its last saved point. Finish all the outstanding races you wish to complete. Access "My Cars" in your career garage. Sell all of your cars except one. The game will not allow you to sell the final car.
Leave the garage and go into career free roam. Deliberately initiate a police chase and allow them to arrest you, awarding you an impound marker. Repeat this process until you fill up the impound marker meter and your last car is impounded. The game will display a "Game Over" message.
Press "OK" and select "Resume Career." The game will then return you to the beginning of career mode, with all of your unlocked items, cars and reward cars intact.
Repeat as many of the game's events as you like, including the 20 defensive races that unlock Cross' Corvette.