hehe. Surface mount buttons
Step 1.
Use your eyeballs, and see if you can trace the traces from the buttons to a 'via' or another component on the board. A via, is a little metallic hole in the board used to allow traces to jump from the front to the back side. If you can identify where the traces for the buttons go to you can move to step 2.
Step 2.
Testing. Grab a multi-meter, and set it to measure resistance.
Each button should have two traces leading from it, put each probe on each of the two wires and press the button. If you have picked the right traces, the meter should show 0Ω while the button it pressed, and something else while it is not. Make sure you identify the required pair of traces per button! (Remember the 'via's from the last step... those are the easiest to stick your multimeter probes onto)
Step 3.
Wiring a new button.
Get some thin wire, tin the end with a little bit of solder, and proceed to join this wire to an ideal spot along the traces for each button. Simply put a new button on the end of the wires and you are good to go
** Disclaimer!
Steps above assume 'Normally Open' button types. A Normally Closed button will behave differently and will require a 'destructive' alteration to the board to add replacement buttons. Be careful while soldering that you do not accidentally bridge any connections, and double-check the connections after you make the solder joint.
The above steps will allow you to simply cut the wires you have added to resume factory operation, and if you do not damage the case, no one can even tell it's been modified!
If the multimeter in step one behaves in reverse... ie. 0Ω, then you press the button and it changes, please let us know. (Digital meters will often show 0L... this is NOT the same as 0. 0L is 'overload' which means the resistance is too high to measure with the current settings.)