if you have 5v your using a wired controller.
You have to use a common ground controller for this mod, matrix wont work very well. By using a common ground, when you make button press you are connecting the side of the button that the controller looks at to ground. So simply hook up your LEDs between +V and the side of the button that is not ground, so that when you press the button it makes a ground connection not only on the controller input, but on the LED negative thus giving you a button that lights up when you press it.