You could try some locusts. Since roaches are illegal I would suggest crickets but if you dont like them then I cant think of much else. I think you just need to feed it something with an exoskeleton. Worms are great staples but they are so soft. When I feed my bullfrog canadian nightcrawlers his poop is soft too. When he eats roaches, crickets or locusts his poop is harded with lots of little bits of wings in it...gross.