I would have all visitors give him treats when they come to visit. Maybe even give them his favorite food to him. He might associate company with yummy treats. Does he have a favorite toy? A feather toy maybe. The company could play with him with it. Just a thought.

When repair people come in my house, my dog goes crazy so I give them Greenies to give to the dog and now she expects treats from the folks coming in... Its pretty funny now, as she goes through their bags and containers of tools, looking for treats!