There is nothing you can do. Even TB port is limiting eGPU for a mid range card.http://www.tomshardware.com/reviews/pci-express-graphics-thunderbolt,3263-7.html
Ah, yes. I've been trying to find that page again. I had forgotten how "inconsequential" the loss was.
Too bad. I had heard TB wasn't much of a solution, at least not one worth putting effort into.