I've never heard of such a thing. Not sure why you would ever do that. You really CAN'T bypass the ECM unless you are going a full stand alone harness with an aftermarket computer. Your engine's electrical components: (injectors, sensors), wouldn't know what to do.
Bypassing the ECM/PCM would be like taking the sheet of instructions for all your cars functions; headlights, injectors, door chimes, horn, lights.... anything that goes through the ECM/PCM then replacing those instructions with a blank sheet of paper.