Unless you mount it lower on the windshield than stock, it requires a new windshield. The sensor goes inside the frame for the rear view mirror (which is a rounded box shape) so its not compatible with the current mirror mount (the dot).
This is how i had mine mounted on the stock windshield:
have a rain sensor specific windshield:
Youll need the following things to make it work:
sensor
frame (unless you change the windshield)
auto-dim rear view mirror (or b8 passat mirror)
trim pieces around the mirror
auto light switch
wiring harness for sensor and mirror
coding