I think it's the only way to explain it as it's been put this way in many grammar books. After all, they are mixed forms of the second and third conditionals.
Once I had problem getting this across, too. If students are involved in the examples about their own lives they get it in a better way. For example, they can be asked to talk about the determining decisions they made a few years ago, and now tell others what would their condition be now if they hadn't made those decisions in the past. (I guess this way they're put in a condition where they themselves feel they need some new structures.)
Also, they might judge the history. They can think about some historical events and guess what the world would be like now if any of those events hadn't happened. We can claim if Hitler hadn't gone the way he went, the world wouldn't be like this now, or any other better ideas!
I'm sure you were not looking for such an idea, but I just felt it might come handy. And I'm open to any criticism regarding this.
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