Sony Z-Series Nvidia Driver Issues

I have a Sony Vaio VGN-Z56GG with a 9300M GS graphic card and I've been trying to install the latest Nvidia Windows 8 drivers on to it without any success.

The installer doesn't even detect the existence of the the Nvidia card on the system, after a bit of Googling I found out that it was because Sony has proprietary drivers for the 64-bit Vaio's with Nvidia graphics. The Laptop is almost 3 years old so I do not expect any official support from Sony and most of the methods described on several forums have been unsuccessful.

Does anyone here have any ideas as to how I can update the driver?