Even I have the Navigation System, I still can't part with my Garmin 10x. I have it mounted on the left vent with an Arkon universal vent mount. I am using a Dell Axim X51v PDA with the Garmin 10x receiver. Not sure of the size of the Nuvi, but I'm sure they would make a similar mount.

I have always used a vent mount or something similar that places the GPS below the dashboard and not so visible to passing vehicles.