Finally got around to getting some pics.
The ebayer i bought the insert from is called 'satnavsolutions' however i haven't seen one on sale for a while.
The sony (nav-u82) unit cost me £175 but you can get it cheaper if you shop around (or get it from ebay). The insert cost me £50.
It was relatively easy to install too, I tried to get a power feed from the micro switch attached to the cubby lid. It didn't work. I also tried to take a feed from the original ISO connector, but i realised that wouldn't work as I needed to keep the transformer on the power supply.
Ended up buying a ciggy lighter extension for 3 quid. Took the power from the power outlet behind the seats, under the centre console and up he side of the stereo (pretty easy in the end).
The unit simply screws to the metal screen holder.
Anyway, here are the pics....