I am speaking only from personal experience here. There may be much better advisers. I personally get those cracks when I'm vitamin B deficient. Usually a few high doses of b will get rid of those cracks pretty quickly. I know celiacs are often deficient in b.
Also, one of my really good friends is a nutritionist. I haven't seen her on a professional basis, but she has told me in the past that those cracks might be indicative of yeast overgrowth, or yeast infection.
So, I guess you could try the vitamins and getting rid of the sugar and yeast for awhile.
eta: When my daughter was first diagnosed that was one of her worst symptoms. They took weeks to clear up (it seemed) but they did clear up. I think it was a combo of high doses of vit B and diet change.