If you look at the Falcon 9 renders on the spacex website, you'll see that the centermost engine sticks very slightly further out than the rest (also that video

If you look at the Falcon 9 renders on the spacex website, you'll see that the centermost engine sticks very slightly further out than the rest (also that video shows the old engine configuration, future Falcon 9's are going to have their engines arranged in a circle with one in the center.) That engine may be on a gimbal that allows a descent that would look something like the LEM's descent. Initial re-orientation in vacuum could be done with cold gas thrusters similar to what grasshopper currently has.