In reply to sjc:
Have been in that predicament twice at Harrisons.
First time I was with a group which came across a guy who was stuck utterly exhausted on the final move on Unclimbed Wall. We talked to him to calm him down and stood under ready to try and stop his head hitting the ground if/when he fell. One of the group raced up and dropped a rope with a loop in it down to him. He couldn't let go to grab it, so he tried to grab the rope with his teeth and came off. We managed to stop his head from grounding and he was unhurt apart from having pulled out half a dozen teeth, some of which were still embedded in the rope!
The second time was a guy on the final awkward move of Spout Crossing. We followed the same procedure, and again he couldn't let go to grab the rope. So the guy at the top tied himself to the belay sling and hung over the edge, with someone else holding his feet, so that he could just reach the stuck climber's head, but no lower to try and tie hime in. We were just setting up an abseil to try and reach him when the guy yelled "Grab my hair!" which the hanging guy did just as the soloist came off, leaving the would be rescuer holding a handful of hair. The now semi bald soloist fell but again fortunately suffered nothing more than severe bruising.