By the way, I'm well aware that comparing Nazgul, Barrow-wights and WW is like comparing apple to oranges to shoes: they are three things with diferent natures. I was wondering if the narrative tool of having a material anchor could somehow be used for the WW, too.
I agree with your suggestion: changing completely the way it works would be the neat way to go. But Since I already narrated a death of the WW (by Orphal), I'm bound to follow this path

What I'm mulling about at the moment is Sauron providing an anchor to the WW in exchange for his servitude. Something hugely powerful, that was destroyed or terribly diminished when the WW was defeated, so that killing the beast was an huge blow to the Enemy.
I'm straying into heretical territory now, but I'm thinking about one of the Seven* (admittedly, some of my favourite "forgotten" topics).
Well, just brainstorming, really. But the beast was effectively killed once in my campaign, and it came back some weeks later, and this I cannot change.
*by the way:
(...)Having an artifact like a Great Ring (see the Nine) might help to preserve and enhance your power/strength (it will likely do so), but once you are killed you have a problem as the item is then no longer under your control (your enemy that just slew you can grab it) and you might face a problem(...)
In another topic there was a discussion about the nine rings, and I think the general consensus was that they were kept by Sauron, and weren't to the fingers of the Black Riders.
So maybe there is some room for a Great Ring as an anchor
