Start at '59th Street' either by choosing it at the 'Chapter' selection screen or by fast-forwarding to it. Whenever you die, or in other words, whenever the game resets the view to 3rd person, don't touch anything until you've switched back to First-Person. This will ensure you don't disable the entire ordeal. Try not to hit the Taxi at the end as this may make you fail the mission which means doing the entire level over again.
During gameplay in 3rd person view when you have nothing in your hands enter the code below which is a combination of action-buttons and the D-pad to activate the infinite ammo cheat. To disable the effect enter the code in again.