i had similar problems, both with my old viper boa, who eventually starved itself to death, but then learned with my solomon ground boa. try anoles, or tree frogs. ive also gotten mine to eat black mice, not the albino lab grade, but the "fancy". ive talked to someone who gave me two possible reasons. the scent may be similar, since it varies between the albino and fancy mice, or the look of the mouse may resemble natural prey. also when did you get this snake, it could be a fresh import, because many fresh imports are extremely stressed they will not eat. it could also be that it is simply not hungry. they have a very slow metabolism, and only eat once to twice a month. as for your ideas, fish is a no, but the tadpoles may work.
best of luck