Hi!
Good idea to have treats for visitors to give him. Start off with them just sitting and ignoring him. You can drop a few treats close to them. Once he has come up to eat those, have them drop their hand down the side of the chair with the treat in it. Continue to ignore him and let him come to them. They can even just drop the treat to the ground, but do it when he's looking at them so that he sees the treat come from them. You can progress to him taking it out of their hand. This should help him to associate visitors with yummies!