From the Bentley manual Page 512-9:
Slide in BMW special tool 00 9 310 or equivalent wedge to lift
motor (B) off mounting plate (C).
This keeps window regulator cable from flying apart.
This is after they:
1) Remove the window glass.
2) Remove the entire regulator assembly from the car.
So, it doesn't really look like a DIY job to me, but let us know if you succeed.