If given lots of flow and a very well scaped tank then you could consider and look into beforehand, South American Puffers. A group of maybe 4 would be ok as they are very sociable with each other. They also tollerate Otocinclus, so you could include a group of them too.
They will more than likely struggle to be weaned onto dry foods. Mine fed exclusively on thawed frozen foods, they wouldn't accept dry foods at all no matter what i tried.
There would probably be options to stock one of the larger Puffers as they're pretty innactive, but probably best waiting for Neale to advise on that one.