I’m sorry, I don’t understand what you require if you already have a JSGF grammar. If you already have a JSGF grammar, there isn’t anything to describe beyond what I said previously:
you can put the words from an existing JSGF into LanguageModelGenerator and use the resulting .dic file along with your pre-existing JSGF. Then you just pass the two files into startListening: (remembering to set isJSGF to TRUE) instead of an ARPA file and a .dic file.
OpenEars doesn’t handle any other aspects of JSGF for you (unlike ARPA) so there isn’t anything else I can give you instructions for.