Excluding an username with an underscore from search results


I’m using this lovely Google script to generate RSS feeds for monitoring client mentions. http://www.labnol.org/internet/twitter-rss-feeds/27931/

The problem is that one client has a handle that looks like this: FirstName_LastName. I have a search for mentions of that, which works fine, but I’d also like to track when people use his first and last name without his handle: “FirstName LastName.” Problem is, the results returned include tweets from his own account (from FirstName_LastName), which isn’t helpful. If I include, via the Advanced Search, in the field “From these users” -FirstName_LastName, it doesn’t return at least some of the results where his actual name has been used, but not his handle.

Any ideas?