This is from the front of the controller board where the potentiometers connect from the back. This diagram is your analog trigger and then you just need a tact on the digital trigger pins, then attach them however you like.
Well you need a switch per each type of press. You could stack the tacts on top of each other or just pick which type of button press is more valuable to you. A lot of Nintendo games rely on both methods but I know for most third party games the digital press will suffice.
Super crude drawing, just make sure that you use zenlocs diagram with it so you don't confuse which part of the transistor is the base, collector, or emitter and you should be fine.
