I have seen a number of things people have used to provide a variety to veggie eaters, from banana, pumpkin, zuchini, cucumber, romaine among others.
The big concern among many would be pesticides, and that could potentially be in something that was wrongfully or mistakenly labeled as organic.
I have seen on Melevs site that his naso happens to love banana, so there are experienced folks out there that do provide alternatives.
If you buy from a store that sells people food/not fish food you need to be careful of what may have been added to it to preserve it or make it taste good to us.