+1 on what fishguy said someone will take it if someone was offering in my area even with the warning I'd take it as all my fish are large and/or semi aggressive. If you put an ad up online you'll get rid of it quickly.
You maybe able to reintroduce him back to the main tank, as the last fish. Also have you tried the “Mirror Trick?” Get an Acrylic Mirror, drill a Keyhole Slot in it and hang it on the outside of the aquarium. I do this, to distract any bullies, when introducing any new fish.