punctuating speech - comma versus period

If I said, "I will go fishing John will I go shopping today." If I take "Will I go shopping today" to be a separate sentence on its own. Is there a way of punctuating it so that the first part "I will go fishing" is NOT being addressed to John? Or is this not possible and by default the first part "I will go fishing" must be addressed to John and therefore the vocative comma must be used, "I will go fishing, John. Will I go shopping today?"