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 question is:

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  How can I disable the discrete GPU from EFI?

  
  

  I assume this is persistable across multiple reboots. I'd also want to know how to undo it if needed.

  
  

Update:

The question is basically whether the command mentioned in GfxCardStatus github issue comment here is correct or not, and how to undo it if it doesn't work.

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An answer to this alone is a correct answer, but it'll be 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 integrated GPU is the one installed and let me use multiple monitors with it?

  
  


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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?