i think i was the first ... possible the only one to do this ?
on my old 1.4 i was fed up of manualy adjusting the mirrors so spent £100 on a pair of electric ones from a cupra.
the wiring.... well that is all down to how good your are at electrics and how methodically you think.
it took me and my dad about 2 evenings (4 hrs total) to buzz out what the connections where on the switch (about £25 from the stealers).
i then had to run a 12v line to the power and run a load of signal cables to both doors.
for this job to be done you will need:
DMM (digital Multi Meter)
correct wiring loom / plug you can molest from a cupra
New covers for the door card (where the new switch goes) both passanger and drivers side.
it can be done, unfortunately i didnt do a wiring guide and i no longer have the car so i cant help you out too much apart from saying.. i have done it and it was the best mod i did to the car, especially when the heated mirrors work on a frozen morning