Can you unplug the primary wire from each coil and see if the roughness changes? ( The 12V wire not the high voltage spark plug wire side. ) This way you can narrow it down to a cylinder. Or unplug an injector wire. When you do this, the computer will likely shut down the injector for this cylinder to prevent car overheating. My car does this. To reset, shut engine off then restart.

If you do find a cyl that does not change when a cyl is disabled, do a compression test, if low do a leak down test.