according to my stealer you dont need to fit a matching pair of tyres, but then they are barstewards! 
http://www.golfgtiforum.co.uk/index.php?topic=56400.0
So, you never got that resolved! 
I'm still dealing with VWCS regarding my concerns too - useless feckers!
No, they basically said that VW don't know (or care) what agreement I had with the stealer, and cited that it was a used car, so it was up to the stealer and its between me and them. The stealers response via VWCS, was like it or lump it as the car is roadworthy, etc etc.
My response was that the car had 4 matching tyres when I put the deposit down. Anyway, I have now put the new non matching tyre on the back, so at least the fronts match. 
That is shocking, but sadly, not surprising. I think any (non-rice) manufacturer's UK importer, be that Reno, Ford, sh!troen, Pukegeot, Vauxhall, etc, etc - would have followed a similar line - not because it was the correct thing to do - but merely because they know they can get away with it.
Did you ever get Trading Standards involved, because, technically, the stealer could be prosecuted under "misrepresentation". I presume you still have all the paperwork, and you could print off the relevent thread!
Regarding the mis-matches - I would strongly be tempted to have them on the front axle. Using the same guidelines regarding new tyres on the rear (for better reduction of oversteer tendancies, and better control when it does occur), and also being on the front, they will wear out much quicker than the rear axle, so you wont have to put up with them for such a long period of time.