I admire your drive to get this done but I think the flaw in the whole idea is that the built-in Nav totally SUCKS compared to basically any aftermarket nav unit, including $150 TomTom, Garmin, Magellan, or even second tier brands like Mio. With any of those units you can program in and find destinations in seconds compared to 1-2 minutes with the iDrive. You'll actually be able to find POI's instead of searching around for which category to search in. You'll have better graphics with night mode, etc. You can actually have usable rerouting options. You can construct multiple waypoint itineraries. Etc, etc, etc. The BMW Nav is an embarassment. Frankly, it is the part of the car that I hate the most.
I second the earlier suggestion to get the double hump dash and then install another type of Nav unit into it.