I don't know how well it works for a serious power-lifter working to improve dead-lift, but I found that HEAVY stepups after a session of box-squats followed by a variation of the dead-lift heavy on the hamstrings helped me get from 350-400. (dead-lift) (I was also weak off the ground). Also what others said about the deadlift on blocks.
I could really feel the step-ups hitting the hamstrings heavy. So maybe they are worth trying out. I tried to go fairly high rep, and until failure on them as well. But that goes without saying.