Hi Emma,
I can understand how frustrating this must be - since you didn't exactly go out seeking them as pets!
First - that wikipedia article shows all sorts of foods that they like to eat. That might be a great source of creative feeding to get them to eat. If all else fails, maybe fishing worms (red wigglers are sold at bait shops everywhere). That would be a common large catfish delight. I wonder if it is the fact that they want their food to move that is keeping them from eating? Dont know for sure. But I sure do wish you luck!
Oh - is it possible that a local Gander Mountain store might want them donated to their tank? My local store is HUGGGGEE and they're always asking fishermen to donate native species. Well, your guys are native. WHy not try calling them? And if they say no, ask who else might want them - zoo perhaps?