Continue what you are doing, you are doing greyt!!! Alone training is very successful.
Is there a trusted neighbor who can check on him or take him for a walk while you are at work?
Leave a radio on when you leave. Don't make it a big production. Say good bye see u later.
Also, you might want to try Rescue Remedy which is sold in Vitamin shops. But if you pupper continues to do well, you probably don't need it.
Good luck and keep us posted.