you are looking into having a new windshield with the light sensor (and/or rain sensor), you can't just install the light sensor onto existing windshield, you will need the correct switch (S8), wiring from the switch to the LCM and the LCM must be able to support the automatic headlight feature, and if it supports the feature, then you need to program that feature to activate it...

windshield alone seems to be: a. cost prohibitive, b. labor intensive, and c. not guaranteed to work...

not sure if the factory solution is feasible - is there an aftermarket option???