If I rememer correctly, MSI has an external case that allows you to use graphics card that uses less than 150 W, but it's designed for Apple devides so you need a thunderbolt connection.
I'll see if I can more info.
Edit:
I've found a couple of articles and forum discussions. I also found another solution, but you need an Express Card Adapter (and a port to use it I guess). I hope that helps you.
http://www.theverge.com/2012/1/10/2698168/msi-GUS-II-external-thunderbolt-gpu-enclosure
http://www.nordichardware.com/Graphics/msi-gus-ii-revies-external-graphics-cards.html
The other solution is this
http://www.villageinstruments.com/tiki-index.php?page=ViDock
And this is a forum where they even talk about a DIY solution, if you dare
http://www.overclock.net/t/983766/discrete-pci-e-graphics-card-adapter-for-laptops-pics
Please excuse my bad English.
Currently gaming on a PC with an i5-4670k@stock (for now), 16Gb RAM 1600 MHz and a GTX 1070
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