I like Nophead's idea, having a thin sheet of steel with a hinge on the side, to eject the printed object you could lift the sheet up to an angle and then bend it till it falls off and slides to the side.
Or have a very thin metal spatula as wide as the print bed to scrape the print off.
Or if you double your Y axis to the rear of the machine and put a wall over it, when the print is done you move the print bed underneath the wall, the object hits the wall, and pop, it's off. When the printbed moves back to the normal printing position, it pushes the object with it's side.