A few years ago I modified a Suncom TAC-2 joystick to work with USB. Click the link below to read the tutorial in PDF-form.
I recently modified it so that the two buttons on the joystick works as button 1 and 2. To be able to use the buttons I moved the direction switches. This way I can rotate the joystick 90 degrees counterclockwise and reach both buttons with my left hand.