I build a power supply (Game On interactive power supply) that utilizes the service outlet that turns on with the game via light sensor relay. It is listed in my pinside shop or on my website. You will need the system plus my 5v adapter if you go this route. I would avoid using the 5v from the machine. The 12v would be fine if you are not running any mods depending on the draw.
http://www.rockcustompinball.com/product-page/game-on-power-supply