Step 1: Open up the Controller Housing and See Where You can Make Connections
So we need to find a way to connect the output pin of each switch to the Arduino. Open up the controller housing and observe how the circuit is laid out. Look for locations that are connected to the output of the button where it would be easy to solder a wire. If you are lucky, you might find unused through-hole points already on the board. But most likely you will either need make surface mount connects or make your own through-hole connection locations.
On my controller I found that there where large contacts at the output of every button. This was most likely used to compliance testing in the factory. I thought that these would make good points to make connections. To make it easier to connect to these points, I drilled holes in each one to turn them into through-hole connectors. This also made the solder joints more secure.