To get all the multiplayer people go to codename and go to 
secret unlocks and type in: Party

Enter these cheats in the "Secret Unlocks" screen.
 
Unlock the Golden PP7 upgrade - AU PP7
Unlock the P2K upgrade - P2000
Unlock the Golden P2K upgrade - AU P2K
Unlock all the Gadget upgrades - Q LAB
Unlock all Multiplayer Skins - PARTY
Unlock all the Multiplayer Modes - GAMEROOM 
 
 
Here are all the cheats I bileive available for this game! 
They are all to be entered in the "Secret Unlocks" screen 
in your codename.