He haven't tried Dubia - roaches are illegal here. You can try to add hornworms too, these big juicy green caterpillars. Don't overdo though. One or two once in a blue moon, they are expensive too. Try mice ( no more then one in a month) , you can try silkworms, but most big frogs don't go eat them - too small and don't move enough.
main diet should be nightcrawlers- sports wholesale sells awesome huge ones for fishing, or any other fishing store.