While I agree with your overall point (I think the thread title is inaccurate), it's an area the Cowboys don't seem to be too concerned about though. Seems like they plan on rolling with what they have, and either Leupke or a TE could play the FB roll on short yardage. That's an option that could help them keep some speed on the field at RB, while also having a bigger body in the backfield to help get push.
Dowdle who is listed at 215lbs could be that guy, the opportunity seems to be right there for him, but he didn't show much in Saturdays game. Not sure what his camp has looked like thus far.