http://www.sandsmachine.com/a
http://www.sandsmachine.com/ac_hard.htm
A 26"*26"*10" meets the USA bag max. limit.
Look at the videos on the bottom right hand side of the Cruzbike Quest Bike page, to see John folding the 22" Quest up and fitting into a Samsonite case with a reasonable amount of room for a larger wheel.
You might need to copy Johns instructions and see what minimum size shape you can create.
Now IF you lived in Australia, the great Island Downunder, then 57" * 32" * 11.4" is the max. size for a free bike box at 23 kgs weight limit (50 lbs)
Super Slim