Sorry to bust your idea but it won't work. How so you may ask? I will tell you. One may take the oxygen sensor and heat it up to say 900 degrees and in the air it will read very little voltage, take the same sensor and subject it to a rich hydrocarbon condition, it will read hi voltage.. thus when you pull the sensor out of the exaust stream you will cause the voltage reading to go down, thus making the computer think its running lean and then it will add more fuel.
Low voltage = lean, hi voltage = rich. Even an exaust leak before the oxygen sensor will make it run lower voltage thus burn more fuel..