On 'Its me or the dog' Victoria Stillwell put a little bit of garlic on the food of some very fussy eaters (poodles or chi - cant remember). These dogs had never eaten dog food and never eaten out of a dog bowl and yet gobbled up the food. She said it is about making the smell more appetising because dogs have a pref for strong smelling things. I often put sprinkle a little garlic powder or paprika on my dogs' food now.
I would probably try Merrick canned if I was having a heavy duty fast going on, with a protein he hadn't had before. It used to be that the thought was canned was bad for dogs, now it's been proven that it's better for their overall kidney health.