The only place I can see a hitch in your plan is with the coding of the actual radio. At this point, is anybody certain that the region coding can infact even be changed? Meaning, is it possible that your UK hardware is physically different in some way compared to the NA stuff? Furthermore, if the programming is indeed re-writable and not a one-time-permanent-coding, can the dealer even do it?
I hate to be negative because your progress is really astounding. Perhaps a BMW Tech on these boards that has experience on the programming side can answer some of these questions. If there is legal issues with a tech posting anything of this nature, perhaps you could PM your thoughts to myself or another member who will in turn post it as from an anonymous source.
2014 BMW 435i XDrive M-Sport - Delivered May 2014
2007 BMW 323i - Delivered April 2007