But if your not a perfectionist and you want to turn that Dragunov into the AK that it really is or shoot the Barrett like a p90 then this is for you. First off you should know that like all other Xbox controller mods there are some risks. First opening the controller voids the warranty (I void warranties), If you do the soldering wrong you could damage you're controller permanently, and if you use it on live I think there is a potability you could be banned (I've played a few games on live so it's not instant). I take no responsibility for the affects of this project. There you go you've been warned.
Update: Two extra peices are required for better performance, a resistor (Gold,black,red,gold) and a diode (I think any will do).
Attach the diode to the wire from the button that goes to Vin making sure that the black end goes into the Vin pin and the silver(-) end goes on the buttons wire. Attach the resistor onto the other wire from the button that goes into pin 4 (it doesn't matter which way resistors have no polarity). Fell free to experiment with other resistor diode combos, if you have one that works well please leave a comment.
I've also included a crumby video for your viewing pleasure (or lack thereof)