We took those giant oversize Zip-loc storage bags, packed them, zipped the zipper almost all the way, then stuck the hose from our central vac in while I sat on the bag to squish it even flatter. After sucking out as much air as possible, we just carefully took the hose out and zipped it shut. It was kind of funny, really, but it sure did the trick!
I guess I thought they open most bags, but I guess not? Maybe just x-ray?