If you want to avoid coding, you might be able to install an inexpensive part that flashes the brake light.
For example:
https://www.amazon.com/Vehicle-Flash.../dp/B00FADDOL4
Installation videos:
https://www.youtube.com/results?sear...se+brake+light
However, I don't know how that product would work in conjunction with the BMW's brake pulsing feature under hard deceleration.