I did a similar thing to my cube speaker few months ago. Instead of drilling hole to the beautiful speakers, I soldered a bright blue LED to a mercury cell inline w/ photo cell. That way the LED acts like a night light. I can turn on/off the LED by changing the position of my desk light. And the whole package is very small, it can hide neatly behind the speaker driver. The only drawback is the battery life. The cell only last a week or so. My next plan is to use rechangeable 'mercury cell' (indoor cordless type), it will be bigger, but still small enough. And change the cell by a solar panel inside the speaker.