Well, whole wheat lembas really wouldn't work, mostly because the bran present in whole wheat flour would cut through whatever light gluten had been formed and result in a remarkably dense texture inconsistent with things Elvish. I mean, let's face it, if anyone exists who refines all their stuff- even their flour- it's Elves. As for lembas made from wheat in general, I've worked with rye flour and flours made from other grains before; you couldn't get a waybread answering to lembas' description from millet, barley, rye, or anything else but refined wheat.