A sort of can of worms...........
If you have a MK4 DVD Navigation unit this will play back the maps in 16:9 format if TV Tuner is disconnected/bypassed,
If its the BMW MK3, Rover MK3 or earlier then no it will in the end revert to 4:3 format, why it doesn't at the beginning I have no idea I'm afraid.
Without the TV Tuner section wired in you will loose other information from your screen to I'm afraid.
Radio Channels display, selections etc.
The wide screen (16:9) Analogue TV tuner is the best all round solution and then add a Digital TV tuner (third party) and view through the AV channel on screen.
You will also require a set of leads for this.
If you have Ã‚Â£500 - Ã‚Â£700 spare of course just buy the BMW Digital Hybrid tuner.