I just discovered how to select an alternate route if you encounter traffic or construction on a minor road, or if you just want to explore. This is on a 2009 X5 35d so the "old" iDrive. Perhaps everyone already knows this.

Select Navigation and go to the third row from the top, this row contains Route List, Route Preference. Keep turning dial and you will find New Route. Select it.

Enter the number of miles that you wish to detour before it returns you to the original route. Of course if you go far enough on the detour, Dynamic Route may just completely re-route you anyhow.