How do I help my neighbors dog?

My neighbors do make sure their dog is fed and watered and has a shelter from the weather but that's it. The poor boy is a golden retrieve, maybe a year old, very well behaved and sweet. But he is incredibly lonely and bored. I try to interact with him while I'm in the yard, my dogs interact with him while they're in the yard. But he is outside 24/7 and rarely if ever has any contact with his owners besides getting fed. I've given him treats and toys and blankets to keep busy and be comfy, and the toys make him happy for a while but eventually he's lonely and bored again. Now the toys only excite him for a few minutes then he's back to his heartbreaking howling and whining.. I feel so bad for him but idk what I can do for him?? Anyone have advice?