The French website Journal du Lapin released an article on the use of an external ViDock enclosure on a MacBook Pro.
This enclosure allows to get access to the PCI-Express line of from a Express Card slot, so it becomes possible to plug an external graphic cards or any devices with a power consumption lower then 75 W. It worked on Mac featuring an Express Card slot, but this is not straight forward, and requires some optimization and hacking.
Performance remains limited due to the bandwidth of the PCI-Express 1x, but they managed to install a graphic card and plug a display on it.
http://www.journaldulapin.com/2012/02/17/un-gpu-externe-sous-mac-os-x-vidock/
