We have an adult WC cornuta (Alice, she is my avatar) and at first she was very hard to get to feed, but with patience, she did start taking the nightcrawlers. She also has had some of the Samurai food. It is excellent for getting weight on them.
What I am wondering is this: If actual breeders and folks with experience are giving you advice YOU asked for, what's the big deal? Feeding it other frogs is going to do exactly what Ra said it would do......guarantee that the cornuta will never want to eat anything else. It is no longer in the wild and why take the risk of passing on parasites or chytrid? We got Alice to eat the worms by using the same methods shown in the video we made for THIS purpose.....to help folks who had difficult to feed frogs.

Best of Luck.