OK, there's some info here
http://www.golfgtiforum.co.uk/index.php?topic=124452.0First, remove headunit facia plate (I used a blunt cutlery knife). Prise the cover off gently as it snaps into place.
Now remove headunit with the four torx bolts
Now unplug the headunit, plug in the fiscon, plug the leads back into the fiscon plug
Wrap the bluetooth box in bubble wrap to stop it rattling when positioned behind the headunit.
Plug the mic into the box and route the cable down through the dash cavity and locate mic where you please.
Bolt it all back together, probably need to recode stereo as well as set up the phone on vag.com