I think you are simply not giving us enough information. The link njarmemka gave you is just fine for building the O2 sensor trick thing (which is what you asked for!!!), this is what you do with the second sensor. You add this thing to it so it fools the ECU into thinking the readings are right. It will work for any OBD-II car (which your car IS). If you are wondering how to hook this all up to the ECU (which will be different for all cars, but VERY close), than this is what you should be asking for - a diagram of the P5 ECU.
Chris