I'm a little late but our vets around here advise to cook Professor Moro's Carrot Soup. It is actually a recipe for children but works wonderfully on dogs, too.
You just beed carrots and water 1:1 (1 kg carrots, 1 litre water for example) and cook it for at least 1,5 hours. After that mash the carrots and add water until you reach the same amount you had in the beginning. (I always cook little pueces of chicken breast with it for the taste).
Feed in small amounts during the day.