That is a lot of weight for him to loose. Corn syrup is a clear syrup that is used in a lot of baking recipes. Over here in the U.S. it is often referred to as Karo syrup because that is a popular brand over here.
Here is a recipe for making your own:
How to Make Your Own Corn Syrup | eHow.com
Do you have a heating pad where you can take the pup away from mom and warm him up?
There is also a 'sticky' at the top of the breeders section for a special formula for weak puppies but you would have to have some liver to make that recipe.