Just spotted Makerbot now have a automatic build platform - http://www.thingiverse.com/thing:4056

I belive what you are looking for is something like what the Makerbots have done with an automated build platform.

[store.makerbot.com]

They have a conveyor over a heated surface. I have seen one in action and it seams to do well with multiple builds. As the conveyor move around it peals off the part and drops it over the edge. The lazy susan Idea is also a good one. Using a similar idea you could simply extend the build platform to make it a rectangle and once one print is done drive it forward so that the back half is now centered and ready to build the next part. this would effectively doubly your build space.

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.