Try bent-over rows as explained here
These have the advantage to make it possible to really controll the work you do by controlling the weight you use. The disadvantage is that you do work not in the plain you would like to to develop your pull-up.
Another option would be to do pull-up negatives at a door (you need a stable one for that). Grap the door on top, get your chin over it (you can use a jump or a chair to do so) and than let yourself get down slowly. Do not use this one for metcons (these can cause rhabdo).
Last option I can add are door rows