Ignoring ethics and legalities, it is possible.
You need to somehow fool the downstream O2 sensor, this is the post cat sensor in the exhaust.
The upstream or pre cat sensor will influence the fueling, so this needs to stay in roughly the same position.
O2 sensors self generates a small electrical signal by the heat in the exhaust gas.
It'll switch between 0.1v to 0.9v, rich (cooler gas = low volts) and lean (hotter gas = higher volts) around once every second or so and this trims the fueling (perfect fueling is a mid way average of 0.45v fuel trim)
The downstream O2 sensor which is fitted in the manifold after the cat monitors the cat performance, it does not influence the fueling.
As modern cars now need to have their emission control devices linked to the ECU and need to be able to warn of malfunctions, if the ECU detects a similar switching signal from the downstream it knows there is a fault with the cat and will light an EML and set a DTC.
You can buy post cat O2 simulators that smooth out the switching from this downstream sensor and I have seen in the past, sensor spacers that hold the tip of the sensor out of the gas stream that have the same effect.
If you're set on removing the cat, I suggest an internet search on fooling or simulating the post cat O2 sensor.
