[citation][nom]blafrisch[/nom]Where's the Z button? I don't see one. This thing is useless if I can't play Goldeneye.[/citation]
I wondered this too at first, but then I looked a little closer to the article:
Thirdparty N64 controller with modded analogstick (no dpad, switch for z and l)
So my guess is the Left bumper (which I can't remember using all that often) on the device works as the left bumper or the z-button based on a slide/toggle switch somewhere.