I have a keyboard hooked up at all times
Personally.... I'd crack that keyboard open and tap off one of the buttons and use that particular button as your coin mech switch.
As Space Fractal mentioned.... a keyboard encoder from Groovy Game Gear is a great way to go, I use the KeyWiz Eco for my jukebox, but mine has an actual full set of functional buttons, digit selection, etc, and I use the Shazaam function for other admin functions like shutdown, pause, volume, clear quee, etc.
For your ONE button needs I'd hack that keyboard of yours unless you have future plans of adding other admin and functional buttons later.... then go with the encoder.
My opinion of course.
