Something you might want to try is just have your neighbour in a room with the dog and you and if Sesh even looks at your neighbour praise him and give him a treat, make sure your the one giving the treat at first. Keep doing this for a little while and then up the ante make it if he goes up to the neighbour and shows a little bit of interest in your neighbour (make sure it's not negative interest though) and then give him a treat. If this works the way I've seen it work he'll eventually go up to your neighbour and might even take a treat from him and let him touch him.

Another thing to remember however is that your neighbour might want to lower himself to Sesh's level and avoid making eye contact with him at first, at least until the dog is more comfy with him.