First, let me say that I have enjoyed your able refutation of the tired old "Christian Country/Christian Founders" argument. Well done.
Still, I feel compelled to present a small point of fact. Religion is mentioned twice in the Constitution. Article 6, clause 3 reads:
The Senators and Representatives before mentioned, and the Members of the several State Legislatures, and all executive and judicial Officers, both of the United States and of the several States, shall be bound by Oath or Affirmation, to support this Constitution; but no religious Test shall ever be required as a Qualification to any Office or public Trust under the United States.
This mention is of course in addition to the more famous reference in the First Amendment.