Spent the day trying to get the wiring just right and had to scrap my original plan because I couldn't get the right signal. But, I finally got an exterior light to sync with the dome light so when I unlock using the keyless entry fob, I get exterior light in addition to the dome light (normal operation is dome light only). It actually comes on any time the dome light does.
It's just 1 very bright LED mounted into the bottom of the driver side mirror arm. Pics were taken inside my garage with doors shut and all other lights out.