"He is afraid of flying. When he flies tomorrow, he should pretend he was on a bus instead of an airplane."
I uttered the above statement in a recent conversation. Of course, I could replace the "was" with "is", but the "was" still sounds reasonably natural. Neither "should pretend he is" nor "should pretend he was" appear in the CoCA corpus, but "should pretend he was" yields about half as many google hits as "should pretend he is", suggesting that it is a reasonably common variant.
So, what are the grammatical properties of "was"? It's not bastardized subjunctive: "he should pretend he were" sounds horrible. It doesn't seem to be conditional either. And it certainly doesn't seem to be past tense. So what role is it performing, and why does it sound OK (even if not ideal) to native ears?