Just wondering, have you tried a small amount of creamed corn mixed in with his mashed potato, or corn meal mush? My son loved cornmeal mush, it was one of his first foods.....of course, I had to get my mom to tell me how to make it, because they don't put the recipe for it on the cornmeal here. Anyway, creamed corn is naturally sweet, and saucy as well, and a small amount mixed in with my sons favorite food worked well.
Also, just as an aside, my son ate sooooooo much food yesterday, he pooped FIVE times!!!! In one day!!! And yes, he is still in diapers. He would come into the room where I was, the scent just wafting towards me, and I was like, Oh, Lordy child!! You have NOT pooped again!!