We were never able to get the defoulers to work on the N54. It was interesting to read that someone above was able to get it to work the the N55.
Reason why the defoulers didn't work (and shouldn't work) is because the ECU is looking for a complex algorithm. Below is a graph showing the difference in signal between the OEM cat and catless...
The White wave form shows a stock reading. The red waveform shows a reading on a catless setup. The waveform actually begins to oscillate without the cat. The only thing a defouler would achieve is make the wave form smaller. It is difficult to explain in lame-mans terms, but hopefully the picture gives a better understanding of why an electrical fix is necessary.