Don't mean to resurrect an old thread but I'll post this in case anyone stumbles across it using the search feature.

I had this exact scenario when I threw together an extra machine for multiboxing using spare parts. I ended up building the machine in a shoebox, which naturally did not come with an on/off button... A quick trip to the hardware store for the cheapest doorbell I could find, and I was in business; worked perfectly.

I had a few pictures but hell if I can find them at the moment.

edit: hmm - found some and made a quick collage