I've been keeping up with this thread and don't know why I didn't think of this earlier. About 8 years ago I fostered a Mini Dachshund who had spent her entire life (5 years) in a puppy mill. When I first took her home with me, she did nothing but pace (common with puppy mill dogs) and wouldn't allow me to touch her. The vet prescribed her Clomicalm, which was originally used for depression in humans. Here's the Google description:

"Clomicalm (clomipramine) is used to treat separation anxiety in dogs in connection with behavior modification and training. Clomicalm (clomipramine) is a tricyclic antidepressant and affects chemicals in the brain (serotonin) that may become unbalanced leading to behavioral problems in dogs."

My little foster didn't have separation anxiety, but more generalized anxiety, and it calmed her down so much that within 6-8 weeks the pacing stopped and she loved nothing more than lying curled up in my lap. She stayed on it for the next six months until she was adopted. Don't know if this would work for Boomer, but it could be another option.