+1 for the tuppaware idea. Get something similiar in shape, slightly larger than needed. Bag it up (3x), put it in the tuppaware then use some pieces of styro to fill the gap between the sides and the top to keep it from shifting a lot.
Then package like usual.
For what its worth, when i worked in a store we would tranship stuff like this in and they would just place it in a bag, then in a box with 6-10 other things and ship it like that. You would usually see some die off around the edges and occasionally some damage in the middle of the colony, but even with that little care they sill shipped 36+ hours just fine from half way across the world.
Its an echinata.