Egpu can also use mpcie and expresscard. Expect the adapter to be ~$113 plus the price of the 7770 and psu. You're going to have to be more specific on the laptop model to know if your connections would even be able to be accessed without having to take apart the entire laptop.
I believe this is the site you found earlier as it was THE place to go for egpu info. Unfortunately it is no longer maintained. http://forum.notebookreview.com/e-gpu-external-graphics-discussion/418851-diy-egpu-experiences.html
Commercial products like samuel posted are a lot more expensive, expect $200+ plus the gpu you want.