Im not sure which code I use but this is how I use it.

Turn on PMN tower, and rapid fire.
Lie down and move forward as fast as you can (whilst lying down)
Hold X
Then the PMNs will stop at a certain amount. and you should have a tower of PMNs that makes very steep steps.

Leave the code on and others can walk up it. Turn it off and the next person to try will be blown up.

Guns are reactivated after the tower is blown up.