Believe it or not, Ricky Williams still has a little gas left in the tank. HB isn't a pressing position presently, but sooner or later the Bengals are going to have to deal with a potential suspension of Benson. Williams is a similar HB and might step in nicely if in fact Benson is suspended, and he might even be helpful giving Benson a few reps off which will also help keep him healthy. Bernard Scott and Brian Leonard are good, but can they carry the load without Benson? I can't expect Williams would call for much more than 1 year at league minimum. So why not?
Naturally, we have other positions that are more important to fill right now, but just throwing it out there.