If you go to one of the Business Centers at a Convention hotel (Contemporary, Grand Floridian, Y&B, Coronado, Dolphin, Swan) you can get computer access. Then, if you can log into your e-mail account and use one of their printers. More than likely if youy have a web-enabled phone and can access the cerificate from the phone they should be able to print it for you.
But Disney has specifically stated in the FAQs that it cannot be retrived by Disney on WDW.