I've got some of those cases knocking about in my junk box, Jon, if you want one I can post it to you.
I use the Sony's with my Karma, I also have the noise cancelling version, which, frankly, aren't worth the money.
I used to get through cheap ones for my bedside radio about every couple of months, by falling asleep and turning over. I mainly listen to spoken word: I've discovered the secret is to take an open top bus tour of Edinburgh, or wherever I am, when I run out, that way we get a couple of free pairs!