I don't see the point, really. People always seem to be going on about the expense of the hub... £600? Madness! Maybe on its own, but it doesn't represent anywhere near that in the total price of a Rolhoff-equipped Thorn.
You could, actually buy any of the Thorn frames on their own and I suspect that SJS would build it up any way you chose. But if you were going to go that route, you'd be much better off with a traditionally geared system - the Shimano hub gears won't have the range you'd want for serious distance.
Andrew