for the mondeo, which uses the same set up, the place on the screen where the sensor mounts is specially shaped so that the sensor doesn't cross any of the heater elements in the screen and it also locates the rear view mirror under the cover

the sensor is actually a light sensor and there are much easier ways to do this than going oem

you may have to search hard for it, but there was a guy on www.talkford.com who made one for his mondeo a while back for just a few quid

hope that helps