So, my question is this. Why can't the amount of oxygen (and presumably all the other component parts of "air") be artifically reduced (by some damnably clever contraption) down at sea-level, thereby allowing the amount of fuel used to be reduced ? In effect setting up an artifical altitude, which could be maintained until the aircraft actually passes through the real equivalent.
Such a damn clever contraption exists. It's called the throttle, and it reduces the Manifold Pressure (MAP), which makes the engine anemic just like at high altitude.