Build a delta.
that's pretty much the build volume of the k280: http://www.reprapmall.com/index.php?...product_id=117

The conveyor belt idea is great. Use it for x axis and when built, just run it round and scrape the print into a container and start again.
Probably would be fairly easy to do.
Apart from the end gcode that rotated the belt a full 360 - and even I could write that. It'd would simply behave like a standard i3.
The hard part is getting the flexible print surface for the belt.

You could get some food industry fine steel mesh and regularly coat it with hairspray.
That could work.
This kind of thing: http://www.bolinmetalmesh.com/info/S...Mesh-275-1.htm