Using BMW Routes & Traffic online you can set waypoints into your route.
Enter Start & End of route and let it give you a route.
Left click on the part of the route you wish to avoid and slide the small circle to the route you want. Let it recalculate. Fiddle if necessary.
Save and Send the Route to the car
This produces a route with waypoints that the car respects.
I suggest that you practice with a local route first.
I have found no way of doing this from in the car.
Not as good as most Nav Systems, but it worked well this summer in an extended holiday in France.
Note - Doing the same thing with Google Maps does NOT work. Despite modifying the Google route and creating Waypoints, all that is sent to the car is the destination not the route.
Last edited by Rogerbu; 10-18-2012 at 10:49 AM.