When my cat stopped eating and I was syringe-feeding her, my vet prescribed valium. It was people-valium and by giving her a small dosage, it stimulated her appetite. It was almost immediate from the time I gave her the valium she would be (voluntarily) digging in and eat on her own.
Is this an option for dogs? I don't have any idea... but I thought I'd throw it out there... Perhaps run it by your vet and see if dogs have similar reaction (I don't know, dogs may not even be able to take valium).