Audi A3 8V: Generate Audio Signal (POI)

Hello,
Does anyone have an idea on how to generate an audio signal in an A3 8V via CAN, similar to the TMC information or the seatbelt warning?

The background is as follows:
Unfortunately, it is not possible to add a POI (Point of Interest) warning system to the MMI plus, which costs almost 4,000 euros. Every basic navigation system, phone, bedside lamp, etc., has this feature .

Yes, I know it's only partially legal, but it's my business.

My initial approach was...
A person takes an old Android smartphone with I/O expansion capabilities and a suitable app, and uses a relay to control the seatbelt sensor.

'However, this would also affect the airbag control system, which I definitely don't want. So, my second thought is to use the contact sensor for the tailgate or the hood instead.'

I find the whole thing very inelegant; it should be controllable via CAN as well, for example, a message in the MMI Plus: 'A vehicle with flashing lights is approaching you on highway A XY' .

Has anyone ever tried something like this before? Where should I start?

Wiring diagrams for the car are available .

Regards,
mc_eddy