While doing weighted pull-ups, I have noticed that my I am much stronger in the first half of a repetition (arms hanging straight -> shoulders/elbows at 90 degree angle) than the second half. In my mind it would make more sense to add a separate set of weighted pull ups just for the first half of the range of motion.
This would serve the purpose of maximizing your lat strength when you have the full range of motion your dyno.
It would still be of importance to work full range of motion pull-ups for when you're a little more locked up/contorted for your dyno.
That's a good point. I was looking at it as a means to improve one's ability to generate when dyno-ing, not necessarily locking off. Then again I suppose this all depends on what one's goals are for the season (i.e. a boulder problem with a huge dyno vs. a sport climb with long reaches)
One option that powerlifters use is using elastic bands to add resistance to an excercise. So in your case just use a heavy kettlebell (or free weight)attached to your harness with an elastic band. The ideal length would let you reach max lock off without lifting the weight off the ground. The advantage is that it adds resistance to the end of the range of motion vs the beginning. I think this would be better training than doing partials, just watch yourself on the negatives.
Another way to add variable resistance would be to use a chain that's partially coiled up on the ground at the bottom of the pullup. As you pull yourself up, more chain comes off the ground increasing the resistance.