The fact that the Constituion does not mention God is evidence that the Framers decided to leave mention of a Creator out of the Constitution.
Now for my next trick, I'll will provide evidence that I did not have eggs for breakfast.
You are tap dancing. Where are the Founder quotes that they were afraid of Christian participation in government? A bunch of guys opened a meeting with prayer every day, and no correspondence or debate exists that documents their wish to separate their own religious practice from the document they were building?
The state constitutions of Georgia, Maryland, Pennsylvania, South Carolina, Vermont and (most notably) Virginia predating the Constitutional convention all have preambles that reference the Almighty. Are you saying that delegates from those states came to the convention and the subject of doing or not doing the same thing in the federal document never came up?
Slight correction to last post--not all the God references are in the preambles, just most of them. For example, Virginia references the Christian religion in their Bill of rights, calling certain Christian precepts a "duty."