Okay, so here's a little mod to the mod:
The lack of noise cancelling that I experienced after doing the mod, comes down to the distance between the ear pads and the headphones themselves. Since you're basically gluing a ring on top of another ring, and the fact that the dekoni ear pads are deeper, the pads will sit further out, causing ambient sounds to get in easier. So I wanted to decrease that distance and bring back the noise cancelling.
I started by cutting the ring off the dekoni pads with a very sharp bread knife:
And placed the ring from the stock pads on top:
After that I started sewing the pads together, on top of the ring. I'm definitely not great with a needle and thread, and black thread would have looked a lot nicer, but it did the trick. I was careful to try not to cover the plastic parts that click into place.
Here you can see the difference in height between the glued on dekoni pad and the one with the ring sewn in:
And the final result:
I then removed the cotton pads next to the drivers, as with the decreased distance they now made the sound a bit muffled.
The noise cancelling is now back, but of course the sound stage has also decreased. So it seems it's either or. But most importantly, the headphones are still more comfortable than with the stock pads.