your best bet is to follow the traces from the buttons to some other solder point in the middle of the pcb. this way you dont have to worry too much about everything fitting together. thats the big problem with doing this kind of pad hack, not a whole lot of room.
id also reccomend, if possible, to cover all your solder joints with hot glue. it takes the stress off the solder and provides a much stronger connection. this is especially good if youre going to have the pad shaking around in your hands.