How am I supposed to run/install acpi_call? I've found a similar solution on the linux hybrid graphics blog, but still couldn't manage to run it.
If you do not know how to use that kernel module, I suggest you to stay away from it. In the past it has been used for disabling discrete video cards directly, but that does not make the kernel aware of the state change. The test_off.sh file should not be used as it's just wildly guessing some calls which may have negative effects on the hardware and software (e.g. crazy fans, lockups).
If you want to disable NVIDIA cads, have a look at Bumblebee which comes with bbswitch, a module for toggling the power of nvidia cards on Optimus laptops. More information about Optimus laptops can be found on Is a NVIDIA GeForce with Optimus Technology supported by Ubuntu?
The bumblebee/stable PPA provides the acpi-call-tools package. After installing the PPA you can open a terminal, load the acpi_call module and perform an ACPI call by writing to the file. This requires root privileges.
Load the acpi_call module and define a convenience function for making an ACPI call:
$ sudo modprobe acpi_call
$ c(){ echo "$1" | sudo tee /proc/acpi/call >/dev/null && sudo cat /proc/acpi/call;echo;}
An example: execute the ACPI method _SB_.PCI0.GFX0._DOD and retrieve the result of it:
$ c '_SB_.PCI0.GFX0._DOD'
[0x80010100, 0x80010300, 0x80010410]
