I agree with those who suggest that Russ Grimm would be a great choice. Check him on Wikipedia - he's got great experience and I think would bring a toughness and commitment to the run game that has been lacking on this team.
Mental and physical toughness have been talked about by Williams, Mularkey and Juron, but their teams have rarely displayed it on the field. The current team does have talent, but it is soft in the core areas - offensive line, QB, D line, head coach and offensive coordinator. Any potential coach must be committed to developing a tough, smart team that is committed to the running game so that the team can be successful in the cold, rain, wind and snow of Buffalo. You have to have that commitment to the running game during all 16 games, not just the second half of the season. Poor weather should be welcomed as a competitive advantage for the Bills anywhere they play. Sadly, that is not the case with the current team.
"When it's too tough for them, it's just right for us!" - Marv