Yeah, preventing the man from jumping given a probability that he really, desperately wants to do it might be the only moral dilemma.

In the movie, 'A Trolley Problem', he should threaten to kill me if I try to prevent him. Or I should precommit to killing all the people he saves if he saves them, so he must kill me to secure the 5 lives. This would be a voluntary sacrifice of my life to prevent an involuntary sacrifice of life.

I suppose 5 people should try to prevent him. If he kills all five of us, he really wanted to do it.

(I'm sure exactly where this line of reasoning became inane, but at some point it did.)