Any book like that should be proofread. It should't be too difficult to add some mark to every dialogue line during the proofreading, and then processing these marks and adding the quotes could be semi-automated. Care should be taken with some complex stuff, like several characters speaking in the same paragraph, or speech spanning several paragraphs, or containing poetry, etc.
You could also leave it without quotes and call it "conceptual". If the writer didn't use quotes, maybe that's what he wanted. Did he use quotes for anything else?
In French, dialogues lines are marked with an em-dash at the beginning, but there is no indication of where the spoken text is interrupted by the narrator, other than normal punctuation, like this:
—What's that? he asked
—It's just some dialogue, she answered, in French style.
—And how can you tell what belongs where? It looks pretty confusing
—Well, you see, you have to read it.
—I asked my friend the same question, interrupted a third person, she answered pretty much the same.
—Gee, this last line is a good one.
Leaving out the em-dashes wouldn't be such a big change.
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