xbox 360 controller mod

i am messing around with my old Xbox 360 controller and thought it would be cool to use my Arduino to make the controller rapid fire. the problem is that i don't know how to take the positive and ground and have them interfaced with my board without the use of a relay. is there any way that i could just connect the positive and negative to 2 different ports (say 8 and 7) and have the board connect the 2 ports on a timer or even based on a potentiometer reading?