I had to do a 'splash & dash' with the Rover this morning, so I had a quick poke around the head lining.
The front of the head lining isn't fixed into anything. There's enough give, so any wires can be pushed over the lip. I also prodded the lining to see if there was a gap between the lining and the roof panel. There is. This got me thinking.
I'm currently working on the idea of : Removing the courtesy light and inserting a wire coat hanger in between the gap, towards the rear view mirror. Once the end emerges from the lining. I'd attach the wires (Which I'll extend) from the mirror, then pull the coat hanger out. Then I'd splice the mirror wires directly to the courtesy light wires. This should save a lot of hassle and reduce the potential for damage to other parts.
The wires on my mirror (from the photos) are different from the guide. I have Black, purple and light green. With the aid of a multi-meter. It should be easy enough to find out what wire does what.