Is she/he wild caught or did you literally get him fresh out of the egg? In my vet science class, we raised a whole bunch from their egg. In the beginning we fed them flightless fruit flies. Then itty bitty crickets and meal worms... As they got larger, we relased most into the green house but kept one, and increased the size of his/her food. It could eat spiders, flies... anything really.
As they get larger, you can feed them bigger prey. I've seen some people actually feed their adults minnows, as in putting the fish in a shallow bowl of water and letting their mantises go fishing... Not to be gross or anything, but in the wild some can eat humming birds when fully grown, so within all technicallities you could probably even feed pinky mice. If he does a bit of research, I'm sure he could figure out more on feeding.
oh, and they love twigs and such... when I was in the class, we kept our big one (probably a girl) in a 5 gallon with a screen on top. It was full of twigs and leaves. Misting the cage lightly during mornings is nice, or simply tossing in wet leaves, because sometimes you will see them drink