The NFL season is long, and Conner's never done it before. I don't think Bell is in game shape yet, and I'm not sure he's the type that would accept a "role," but he'd be getting paid either way.
It's not like you can use the money elsewhere this year so I think he'd be great to slowly work in, and limit Conner's carries over the second half of the season. Plus his skills as a receiver means there are certainly situations you could play them together.