Hello Everybody!
I have problems too...
What I got:
Lenovo T520, i5 2520M, 16GB RAM
dgpu: NVS 4200M
egpu: GTX570 (tested on desktop)
PE4L 2.1b + 350W ATX
After purchasing PE4L I updated BIOS and happily connected to HD5670. Today I recovered my notebook to be sure nothing from radeon drivers left. And for few hours I'm trying to connect with my GTX570. I have no errors in device manager, Both, egpu and dgpu are visible, but still no signal on external monitor. I tried uninstalling dgpu and installing drivers in many combinations, with dgpu enabled, disabled, older drivers etc. And strangely CPU-Z is showing egpu like it shows dgpu without drivers (-250MB of memory). I wanted to try custom verde drivers but couldn't find custom nvam.inf file. Any help is appreciated. I was so happy to play some games this holiday ...