This involves editing a game file; create a backup copy of the file before proceeding. Use a text editor to edit the "*.plr" file corresponding to your player in the game folder. Add the following lines under the "[GAMEOPTIONS]" header.

REWARD_Medical_and_Safety=1
REWARD_2_Seaters=1
REWARD_ThemeArt=1
REWARD_CertificateLevel_0=1
REWARD_CertificateLevel_1=1
REWARD_CertificateLevel_2=1

Doing this will unlock the Medical and Safety cars, the 2-seater training car from the school mode, alternate backgrounds in menus, and marks the 3 training school phases (Indy, Monza, Suzuka) as passed.