When Mendenhall has a lead blocker like Miller or Johnson in the backfield, he reads their block and tries to find a crease where they have blocked.
When he is the lone back in the backfield he has to read where the hole has been created by the O line. When there is no hole, he tries to be patient for one to open up and sometimes gets caught for a loss. I guess that you are advocating that if he has no hole to hit, he just drive his helmet into the back of an O lineman. That is one way to motivate them to block I guess.