Well, the extension refused to install, even when I added the Tampermonkey browser plugin the extension was arrested and locked away by my anti virus for looking too much like a malicious program.
Been mocking around a bit with the search engine and it seems just adding - in front of a username removes their submissions, but the search engine fails to find anything when - is placed in front of a username that already has - in it, like -john-smith. I guess the engine treats this as a case of two usernames without an empty space between them and tries to look for anything submitted from those joint usernames.