Make him actually an avolakia who is using polymorph self. Have him speak highly of his beautiful homeland in the Underdark, his people's persecution by the Duergar, Drow, goblin-ken, gnomes, and dwarves.

Have him invite them there, and serve them a dish. Be sure to place a few red flags along the way.

Under the platter lid, is a mound of moving rotten zombie heads staked to the tray. Some animals, some people. Writhing and moaning. When the players are taken aback, have him patiently explain that it's considered rude to refuse an offer of food(given its scarcity); that it's seen as an invitation to be eaten or sold as slaves to the mind flayers. He then sits down and begins eating. Between mouthfuls, he says "so, my friends. Do what seems good to you."

Only reveal his true form if the players attack. If they go along with him eventually he either sells them to the mind flayers or makes them into zombie cattle.