Changing the dictionary will not be enough. You have to create both dictinary entries for your words and include the new words in the language model - in your case the JSGF grammar.
You will need to determine how and when the new words appear in your application and create appropriate jsgf definitions.
Alternatively, you can create a n-gram language model (even with unigrams only). It can be generated automatically based on your corpora (using lmtool
from sphinx utils) or you can create it manually.