Get two normal bike boxes, cut one end out of each box, slide one box into the other and use copious amounts of Duck tape to seal the join and give the whole box a structure, ime four rolls do the trick.
IIRC the max length is 210cms, provided you don't exceed this length (and the width and depth) you can ship the bike still as non cargo. With this method, provided you move in the boom and remove the chainset you can probably place the bike in whole although you may well have to take the seat and tiller off.