I've done this on my mk5 sport and tbh....piece of piss...lol
get the windscreen changed from a proper place (get it done through insurance and when you ring tell them you have the rain sensor, they'll send the rain sensor one, but make sure you have the correct rear view mirror to hand)
i got the mirror/sensor wiring out of a wrecked GTI so got kinda lucky, otherwise you have to makeup the loom as per that guide
shammy, no need to have the roof lining out! just tie the end of the new wiring loom to a wire coat hanger and very carefully poke it out toward the end of roof lining with the grab handle removed and you should be able to fish it out then run it down the a-pillar, under the glove box, behind the stereo and steering wheel and into the CECM, plug into the correct pins and away you go! easy peasy after a bit of vag-com!
i've retrofitted a load of stuff to my golf my self, at the moment in the process of fitting auto-levelling bi-xenons, headlight washers, low wash fluid and TPMS all in one go using a wiring harness i'm making up myself from salvaged connectors, pins from the parts counter and salvaged connectors from the breakers....easy peasy with elsawin at hand!lol
Shammy, are you fitting fogs the 'proper' CECM way or using a relay?