Often cresteds get 'addicted' to baby food like snakes do to mice. Really the trick is to be consistent, feed him in the same spot every day and not change the food brand/flavour too much. IMO the best MRP brand is Repashy Superfoods Crested Gecko Diet (available in bags and T-Rex bottles). Keep in mind they won't starve themselves and often you don't even notice that they have ate, depending on the consistency of the food itself, and how many licks they take lol. I'd say just keeping trying, be persistant and don't change your routine. I know someone and it took almost 2 months for them to get their gecko to completely switch over! Eventually the geckos realize they aren't getting any more junk food and switch over. It's not that they don't like CGD - mine love it - it's just that they would RATHER eat that crap haha.
If you want to make sure he isn't just stretching himself between cricket feedings, cut the insects altogether until you know he is feeding well on CGD.
Repashy is also available in 2-part diet which is the base, with all the good stuff, and flavour, which sweetens and adds...flavour
There are about 10 different flavours so it gives you lots of room to experiment with what your geckos like. The 1-part mix however has rose, strawberry, banana and mango (or fig I forget) all mixed together and I find it to be a big hit. If you put the bag (unmixed) in the frisge it lasts like a year so it won't go bad on you.
Another thing you could do is mix it with baby food in decreasing amounts to get them used to thew taste. This works, but I'm not a fan. Baby food is junk to geckos and it messes with the nutritional balance of the CGD.
Alternativley, you could feed the smoothie mix with crickets but it is way easier to feed the CGD because it is hard to get the correct nutritional balance by yourself.
Remember to only feed crix about twice a week
Hope that made sence I've been a little out of whack today.