External Graphics adapter for laptop

[gezus101]

Is there any graphics adapter (USB) that uses the discrete graphics of a laptop?
I have an HP ENVY with a 4700MQ, 12 GB of ram and an Nvidia GT 745M. I want to run a dual screen setup and autoCAD on it, but there is only 1 HDMI output, no DisplayPort. I have an EVGA UV+ 39 hooked up right now, but I've been told that using it disables the discrete graphics card and forces the HD 4600 to kick in. Is there a graphics adapter that won't do this?
It doesn't have an external PCI-E slot.

 

[Brunostako]

There exist USB 3.0 adapter for additional screens: http://ecx.images-amazon.com/images/I/511S4GAu2lL.jpg

There's also a DIY way to connect a external GPU to a laptop trough the PCI-Ex 1x inside, replacing the WiFi card.