Anti-keywords

I have several pages on my site that get hit by search engine queries that are mostly unrelated to the content. (Most frequently found is a previous post about search terms… determining why is left as an exercise for the reader.) Rather than mark the pages uncacheable or remove them entirely, I’d prefer to add anti-keywords that search engines could use to remove the pages from their results for those queries. There’s a short discussion on this at Webmaster World, but no real solution. Anyone have any brilliant ideas?