Disable dual Graphic and use only Intel card
The only way to disable SIP is to go in through the recovery partition and disable it from there, so unfortunately I don't think that will be an option for you with the current state of the machine.

I would take a look at the answer for this question here:
MacBook Pro How To Disable Discrete GPU Permanently from EFI

Booting into a different OS is probably going to be your best chance at success. Hope that helps!