maybe you should just dust the crickets with the vitamin powder since those are his favorite insect. that way he is most likely to get some of it in his system.

if you want you can add some baby food to his cgd until he starts eating it well and then gradually decrease the amount of baby food your are using until you are back to mixing with plain water. the thing with cresteds though, is that if they know they are going to get their favorite (crickets or whatever it might be) they will hold out for it. so if sprocket gets crickets regularly enough to expect them on a certain schedule he will skip the cgd on purpose. you wouldn't think they would be able to rationalize that way but believe me, they can!

silkworms or phoenix worms would be a great food item for sprocket. maybe you can try them both and see which he seems to like best or what is easiest/cheapest for you to keep.