I really don't think the analogy with quantum mechanics is useful, and may even be accurate. Just say what you want to say without the analogy.
Then you have chosen to risk the life of those on the train, as well as any who may be in the resulting path (which could even include our original victims!).On a separate note, my decision would be to try and throw the switch at the exact point where it would be impossible to know which way the train would go. My thinking is that I may derail the train, and if I don't succeed, then at least I tried, and fate decided who would die.
This solution seems... inherently suboptimal to me. I think for it to be the moral choice only happens in a very narrow range where a "higher power" needs help to affect the situation, and you are morally compelled to take action, but oddly not in a way that minimizes loss of life.