Thank you, that was a great idea. I installed the Intel Driver for Thunderbolt, but sadly it still does not recognise the device when attached. I also did some poking around the Bios and I can find no mention of Thunderbolt either, which I think other G750 users would normally see (if this was available). I did come across another post that said it is marked clearly with a Thunderbolt logo next to the port. This does not...
It looks like either finding a donor motherboard, with Thunderbolt, or upgrading the laptop are the only options. Real shame this is not standard on all the gaming ROG laptops, none of them lack the power to handle it... Hopefully this will soon be a thing of the past.
Thanks for your suggestions!