Just to preface, this is completely unsubstantiated. I haven't read this anywhere besides the inside of my own cranium. But what if we moved Isaiah Bell to fullback? We know he's athletic (came in as a relatively highly rated safety) and we know he's big (roster lists him at 6'1" 245, about the same size and Demens.
What we think: Bell will only be a RS soph this fall, but is presumably passed on the depth chart by guys his own age or younger at some LB spot (Ryan and Mike Jones). Demens is only a year ahead of him and has locked down the MIKE spot, and we're bringing in a slew of young talented LBs in this class.
If we decide that he'll likely be a back-up, why not have him hold down the starting FB spot for a few years? His size and athleticism would be great for that spot.