lol i tried it too, but didnt work. heres a cheat that u dont must press arrows in the
d-pad. ok there:
1a) DONT GO ON XBOX LIVE, BUT GO ON THE SOLO MODE OR IT WONT WORK.
1b) Choose the difficulty that u can do anytin what u want.
2a) Go in bot optitions where u can decide what bots can buy.
2b) disable everything in the bot opitions.
3) select a level. (the level fastline is best so choose it.)
4) now EVERY BOT cant buy anything! too ur teammates.
5) only u can buy weapons.
6) have fun with that cheat.

NOTE: when u die, the enemy who killed u could pick up ur weapon. watch out then!