I would not back lead or change the weight on my own or guess what he was trying to lead and execute the step on my own. If it did not work, it did not work. We have to agree that it happens, and it does not have to make the leader (or follower for that matter) feel "poor".
There are better ways for a follower to help a less experienced leader, among them, knowing the music very well, having a great balance, not noticing and counting his "mistakes", being relaxed, calm, and patient, including in a most physical way -- waiting for the lead instead of guessing the step and jumping into it...
Interestingly, I find when I do that, very often the lead becomes clearer, people dance better, and the whole thing just works out better.