Excellent suggestions so far. It would appear that rack pulls for the most part only have carry over for a smaller number of lifters that you would think. If the goal is to bring up your lockout, upper back work is probably the best option. Heavy and high repped dumbbell rows, shrugs/power shurgs, etc. seems to help a lot of people including myself. But back to rack pulls (and possibly block pulls), give them a try and see how it works for you.
As for the comment on the clean and jerk. It is an excellent movement, but it shouldn't replace any of the big lifts. Strength can and will be developed on the movement, but decent numbers also rely heavily on technique. Front squatting 405 is much different than catching 405 in a full clean and squatting it.
Those that master the movement (olympic lifters) still rely heavily on training the back squat, front squat, clean, jerks and push presses. This isn't always the case for the olympic level weightlifter but they have already developed a huge foundation with non-competitive lifts and partials.