Bring out your one man army bag but don’t select a class, press the PS button and go to messages and join an old invite from somebody. Now your get an error press ok and now you can run around and knife people while having the bag out
BTW! you can also use the same method in hardcore matches, to have a radar on all the time.
Just click start, and find a MW2 invite you never accepted, and you get an error, and the start menu will be up until you exit out of it, but you can move around .