Not finished yet, just a rough knock up, on a pair of old mirror glasses I have.
You have to cut the back plastic of the mirror housing and through the heater element, as such you loose the last 30mm of the heated mirror but it soon clears conducting the heat across and the rest is unaffected.
Once through that you place the indicator leds directly on to the back of the glass, fill back in with black mastic. Totally undetectable from the outside.
Wired through the door and up through the wiring convoluted tube to the body and connected into the wing repeater ( this is not on the bulb failure circuit so no problems with that side of things