Welcome to NICO. There are a couple of companies that offer a product that is installed behind the center switch )(NAV, air/con, etc) The harness is connected in between your current harness connections and they fit exactly. Infiniti has a safety feature that prevents many uses of NAV, setting, etc when the car is moving, is not in "P", or does not have park brake set. This gizmo by passes the safety feature so that all functions of the system are usable whist driving.
Here is one of the sites who offer this bypass:
There are videos on YouTube that walk you through installation:
I have not done this, but I have dismantled my dash, removed and replaced most pieces and parts when I re-covered my dash and this looks much much harder than it actually is. Just remove a little trim, unplug the center switch, connect the harness, and Bob's yer uncle.
NOTE: This video is based on a newer model with a slightly different dash. The 06 & 07 models are easier to take apart, but you must first pop off the small trim piece that lays above the start button to remove the main center switch.