I once had some extremely tough seeds. Filing them a bit worked. I also had success by carefully filing and then prying a seed open and taking out the embryo-baby-fetus-plant... whatever you wanna call it.... kinda like performing a SEED-section. Then put it into the damp-paper-towel-tupperware-incubator and it started to grow fine without any damage. I did a few like that to make sure it would work; thousands of bagseeds are fun to play with!