Courtesy of the Evo How-To forums, it's cheap and easy.
Mechanical o2 Fix
This has been done on a Ralliart and it does work. Remember, do this to the rear O2 sensor, not the one in the downpipe.
The basic concept of this fix is that by moving the O2 sensor out of the exhaust stream, fewer exhaust gases will be read by the sensor, thus tricking the ECU into thinking there's a functioning catalyitic converter cleaning the exhaust.
Make sure you do this to the second O2 sensor in the midpipe, not the first sensor in the downpipe.
