I mind a gorgeous greyhound once or twice a week. Sweetest, gentlest dog ever but after a couple of hours, just becomes inconsolable - whining, howling, waiting by the door for his owner to come back.
I find that he has no interest whatsoever in play or toys. He just sort of looks at them then walks away. I talked to his owner and she agreed, he's never been interested in them.
The only things that temporarily cheer him up are treats and lots of petting, so I do that but I worry that I'm just reinforcing the anxiety. His owner really has no advice other than to say I can call her to come and get him if I need to. If possible, I'd rather figure out a way to cheer him up though.
So to summarise, things I've tried are offering him toys and trying to engage him in play; trying to take his mind off it by doing basic commands with him; and finally give up and give him treats or rubs. He just looks at me like I have two heads. His owner says I don't need to walk him because she walks him before dropping him to me and after picking him up about 4/5 hours later (he's free to come and go in my back garden as he pleases when he needs to piddle).