You can gut load snails with dark green leafy veggies, carrots,etc to increase their nutritional value. They're a good source of calcium, moisture and low fat protein. Flies can also be gut loaded with fruit, baby food, etc.
Since you hate crickets, gutload and try to get him to eat the roaches.
How are your temps? My Jackson's HATES any temp over 75 degrees and won't eat. Mine is most comfortable (his neutral light green color) when the temps are between 65-72 degrees.
Also, mine won't eat unless he's hydrated. If his tongue is dry/he's thirsty his appetetite decreases, so make sure your's drinks..alot. They love water. In nature, the leaves are usually covered in dew first thing in the morning that allows them to hydrate / moisten their tongue before they begin to hunt.