So your position is that Congress, by statute, can define what the terms of the Constitution mean? Really? I don't recall that being one of the enumerated powers of Congress but I'm sure you can point me in the right direction.
Title 8 of the US Code can no more inform what the Constitution means by "natural born citizen" (and makes no attempt to do so) than Congress could by statute define what the terms "due process" or "privileges and immunities" mean.
You may be a lawyer, but it seems you're a bit rusty on your Con Law.
. . . adding, I'm not saying McCain is not a "natural born citizen" and I'm not saying that anyone will or ought to challenge whether he is a "natural born citizen." All I am saying is that it is an open question, as his campaign acknowledges.