There are two types of O2 sensor simulator,one is electronic base and other is mechanical type,usually second one is very simple and easy to fabricate.
Buy two spark plug adopter and widen its hole by using a thick drill bit,remove O2 sensor and install both the adopter on the O2 sensor port, then screw the O2 sensor back into those adopters.
It slows the reading down on the secondary 02 sensor by moving it out of the exhaust flow thus fooling the ECU into thinking the CATS are still in it.
You can fabricate that adopter by a machinist(Lath walla) and its length should be in between 2 to 2.5 inch.