Option 1:
Get the dealer to install the UK settings. In this mode, units of measurement are supposed to change as well (yards, km/h and others I am told).
Option 2:
Install an older version of the NAV software, and then a newer version afterwards. There's supposed to be a 'bug' that removes the disclaimer screen. New version is V-19 according to the bimmer.roadfly.org board
Option 3:
Look at
THIS LINK for information on a module that will do it for you.
Good luck. I haven't tried any of these BTW