Apparently you can buy special 'electrical' paint on the internet to re-paint the buttons as it is this black material on the underside of the buttons that completes the circuit on the circuit board and registers as a 'press'. At $25 a bottle however, I cheaped out and bought a small bottle of 'rear window defroster' repair paint. This is used to repair the 'metal' lines on your rear window defroster to complete the circuit and works pretty much the same way on the buttons. I got mine for about $8 at an automotive store.

The only negative I've found is that the paint is really not meant to be 'pliable' when the button moves, so over time it can sometimes flake away and you have to re-apply it. You also have to really clean these flakes off or else they will affect the operation of the other keys. (Randomly completing circuits!)

The only other option that I found on the net was some guy Krazy glued small pieces of tin foil to the underside of the buttons. The tin foil was the same idea as the electrical paint so pressing the key then cause the tin foil to touch the circuit board and complete the circuit resulting a button press. Same theory, just different material.

Of course if Harmony would just sell you a replacement keypad at a reasonable price, that would be easier. I've never thought to ask so that's another option.