Adding vocab on the fly

[Manjunath-mlp]

I am trying to implement adding external word on the fly instead of rebuilding the main decoding graph.I was exploring grammar fst of Kaldi.I am thinking of predicting the outputs from main decoding graph and external graph(which i prepared from external words those are not present in main decoding graph) parallely and replacing target words with external graph predictions.Any better approach or this works?