Use whole dictionary file with Julius or return null

I have successfully set up [Julius](http://julius.osdn.jp/en_index.php) to work with my own grammar and .voca files. The problem I have is that it always returns a suggested response, even though the phrase uttered may not sound like anything in the .voca file. I would like to find a solution to either return null if no match found and/or use the whole dictionary file to pull words from. Can anybody help me with this or at least point me in the right direction?