Forum staff don't have that ability, and it is extremely unlikely that an ingame petition would get any response for something like that, either. If you want to give it back that badly, just let him capture your town and take the guy back, just make sure you don't run out of gold (although I am not sure what happens to "captive" heroes when somebody else conquers the town...) chances are if the hero isn't destroyed, he would also have to recruit him back.