I feed mine a little canned food mixed with kibble once a day and then they have dry kibble out all the time. I would put the missing link on the canned food because then you can mix it in. I bought some but as yet have not been able to figure how to give it individually to 4 dogs who think eating out of the same bowl is more fun than each having their own.
I put 4 bowls down and they all crowd around the same one. Go figure!
Stick with the premium dog foods -- they usually have more digestible protein and may help a lot in putting weight on your little one. I use Canidae and Chicken Soup, sometimes Nutro.