They just use another layer of them growled at a different pitch at the end of Master's Apprentices, and in a lot of places on BWP (most obvious is the part after the interlude in the title track). I think he whispers under them in the first part of Demon Of The Fall to get that effect.
They're more just production techniques, than actual vocal effects. I don't think I've heard any bands that cheat the growls though, so I don't know what that even sounds like. Who does?