Have you tried leaving a radio or tv on for him?
As for the drugs, that's why I prefer herbals, they are usually cheaper, don't require a script, and their use can be longer without negative health impacts.
Really exhausting the little rugger can help.
Have you figured out whether the dog likes ANY treats? Sometimes you even have to try "human" foods like cold cuts or pieces of real meat. Hopefully you can find that special treat that will work.
Yeah, it's tough. I think my dog had been sooo used to being surrounded by the breeder's other dogs and had that "crutch" when the breeder wasn't around she was never really alone.
Patience, patience, patience.