So I finally received both the OEM cases in the mail, and thought I'd mix a hybrid of the two; I like the look and slimness of the Flip case, while I don't like its adhesive application and want to be able to swap sim cards more easily.
You can see the adhesive side in the inside of the Flip case.
The smooth finish on the back of the Hard Shell Case.
The hybrid!
Alas, it doesn't work quite as well.
As it turns out, it becomes a little too thick for the case to close comfortably. It's definitely a workable method and it feels a bit like the Otterbox Defender cases. But to me, it just was a little bulky to carry around in pockets. Guess I'll just use the Flip case alone and keep the Hard shell case for when I need it.
I don't think it is an adhesive as such, I have a dash mount in my car which has a polymer pad which displays adhesive like properties and think this is something similar
They've been available in eBay UK by some sellers. The one I bought from has now sold out of the stock (as they usually tend to), but you can get one from here.