Have an iMac with thunderbolt, will a PCI converter with a better GPU work?

[adagio]

I have a recent model 2.9 GHz Intel Core i5 iMac with NVIDIA GeForce GT 650M 512 MB graphics card. It's a bit rubbish for mining purposes as most people will know. I had the idea of buying a Thunderbolt:PCI adapter, something like this (though not necessarily this brand/model) http://www.creativevideo.co.uk/index.php?t=product/sonnet_son-echoexpse and plugging in a mac compatible card, something like this http://www.tomshardware.com/news/Apple-Sapphire-Mac-HD7950,21610.html

I'll looks around for the best prices etc. and work out whether it's actually cost effective later, but at this point I just want to know if this is even an option and especially if someone is already doing it

Thanks in advance

[Wed]

That's a great question.
Can anyone help?

[adagio]

Not completely stupid then, that's relief It would probably be a bit expensive but cheaper than buying a whole new rig and/or learning to use a PC again. I've done a bit of reading around and it seems possible. The biggest problem appears to be that the cheapest chassis only take smaller PCI cards.