I'm not sure it's correct, but it makes a lot of sense. One of my options (again, not sure if it's correct, but it's very clear) is to use italics for any speech that's remembered or imagined:
And why would I want to do that? I hear you ask.
And Luisa, I'm interested that you're partly going on the inflection, rather than the grammar. When my punctuation gets picked up by a copy editor it's nearly always because I've punctuated for how it would read, rather than what's correct. Maybe it's partly because - like Nikki's example - I'm almost always writing in someone's voice, and hearing it as I write.
Good point, Emma, and I've course I'm biasing this towards the way I write, which is always very strongly in someone's voice. (Like Nikki too, I'm pretty sure.) I'm going to get copy-edited to bits soon.
Of course, Nikki asked for 'the correct way', not for my descriptive opinion. Sorry, Nikki!