are you going to need a mouse or you have a touchscreen. what would you want the right and left click buttons to do? you could always implement a usb touchpad on the wheel. and still hack a mouse for the scroll whel for the volume control.
also what make and model car do you have. most cars possibly higher models of your car do have steering wheel controls. usually plug right into the cable reel. you might be able to find one used and interface your left and right buttons from the mouse that way.