Hm... I don't keep Cope's, so I'll let other people with more experience give you info on what might be wrong. Other than that, like someone already said, most frogs are attracted to motion when they eat. You could maybe cut the tip of a nightcrawler's tail off and let it thrash around? May not work, but they won't hurt anything.
Also, get him into his permanent enclosure as soon as you can. If the storage bin isn't vertical that could be your issue. They don't feel comfortable when they can't get up high.