Most of the small spiny eels are fine with small fish and wont make any attempt to eat or attack them. You could also try some mini catfish like the south american bumblebee catfish (which I have a tank set-up for, and once settled theyre really fun to keep) or some of the smaller asian stone catfish. Have a look at the pinned topic at the top of the oddball forum, theres and anti tankbuster topica, thats the best place to start.