There are alternatives but generally a "whole food" diet ie roaches,crickets,mice,rats, is the best way to feed monitors so they may not meet your criteria. Becuase you choose tegus/monitors I am guessing you like the "look" and or the way they carry themselves. With the size of your enclosure there are some really cool lacertas floating around. They have the moitor/tegu look and people that have watched them in the Canarys say they act like "little komodos". They also utilise fruit in their diet(still the staple should be whole foods). Another benefit would be becuase of their small size you'll get to watch the behavior you may be looking for. Just a thought, good luck in finding the right species. (quick note: I do not breed or even currently talk to anyone who sells lacertas,monitors or tegus...just think lacertas may be an option)