Enter the following as Player Four's name. You'll hear a buzz to confirm:

world class        A8 Championship available
turbo challenge    A8 cars available in Time Trial and Single modes
max power          Citroen Saxo WRC
throw me a bone    Citroen Saxo WRC
give me time       One minute of extra service time (press 'T' at the service screen)
arcade unlimited   Energy in Arcade Mode
arcade action      Arcade Mode surprises
group b            Bonus car
mooserati          Bonus car
lambaaghini        Bonus car
spud car           Bonus car
precious things    Bonus car
furry dice         Bonus car
mf hotback         Bonus car
tree hugger        Bonus car