There's no big deal in implementing obfuscated_article, just get the soup with self.index_to_soup passing in the url, make whatever changes you want. Save the soup to a temp file and return the path to the temp file. The rest of the recipe processing will then take place as normal on the contents of the temp file.
But if for some reason implementing obfuscated_article freaks you out, you can re-purpose populate_article_metadata to do what you want. Though IMO, that's a lot more hackish than using get_obfuscate_article.
Or you can implement preprocess_raw_article() which has the URL available.