When a crested gets the taste of crickets on his brain, little esle seems to do. I would recommend feeding him crickets twice a week, and providing the t-rex formula every other night. I mix mine with a peach flavored baby food, but you can try all kinds of different flavors. A lot of people say that bannana is a favorite, buy my female won't touch it. All of cresteds seem to like peach though. In the beginning I would mix a very small amount of the t-rex food in with the baby food. Over time, work to add more t-rex food to the mix. You can also get yourself a small syringe and suck up the baby food, and squirt a small dab on their nose. They will lick it off, and when they do, you drop some more there, until they are no longer interested. You can also offer it on your finger, and most will lick it right off your finger.
Good luck!