replace long comment exchange with a brief resume An user commented this question, I commented his comment, he commented back and so forth, and it took seven comments for me to understand what he was suggesting.
Now, that long comment exchange seems quite wrong; I'd like to throw it away, replacing it with just one comment, or incorporating the suggestion in an edit or the like, because it is of no use for potential answerers or for future readers.
Is it possible, or is there a better way to clean up the discussion?

If the information within the comment adds good information to the question which would help future readers, post a comment to the answer with an understandable summary of that information. Then flag the post for moderator attention and explain; mods can easily delete the extraneous comments and clean up the post. 
You might mention the username of the person who gave the information, though, since it was their idea.