Macbook Pro: How to disable discrete GPU permanently from EFI?

I'd like to disable the NVideo GTX 750M GPU on my Macbook Pro 15" (Retina, Mid 2014, OSX 10.10 Yosemite).

I know I can use GfxCardStatus but I read I could have a more permanent solution by changing some EFI flag.

My main question is:

• What is the command to change the EFI to disable the discrete GPU persistently? And what's the command to undo that if needed?

This alone will be a correct answer, but it will be really awesome if you can also tell me:

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  If you force integrated graphics in GfxCardStatus, Mac OSX (up to Yosemite at least) doesn't allow you to use multiple monitors (even though the built in Iris Pro can do it).

  
  

  If I disable the discrete GPU from EFI, will Mac OS think discrete is the one and let me use multiple monitors?

  
  


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  I heard that the same EFO doesn't even show the integrated GPU to other OSes than Mac OSes and you have to trick it somehow to think it's Mac OS. Is that true? And if yes, how to do that?