Badger,

Try leaving a radio or TV on for him when you leave. Also, ask your vet about a DAP collar. These are wonderful and do work. They are composed of natural pheromone which are released as the dog's body temp increases due to anxiety. The pheromones have a calming effect on the dog. They do have to be replaced every 30 days (the only draw back given they run about $40 each).

Good luck and keep us posted.