So, I just had to register to the forum to give a big thumbs up to this guy for posting the code snippets and to give some advice of my own.
I just recently acquired a 17" Macbook Pro (Early 2009) with Nvidia 9400M / 9600M GT graphics. On the primary HDD I installed the newest 10.14. macOS Mojave (using the dosdude1 patch) and on the secondary HDD (which replaced the ODD) I installed a vanilla Win10 x64 1809, using uEFI.
I spent all day yesterday and half of today trying to get both of these graphics adapters to show up and work in windows, one at a time of course.
It found out that while I do still need to pass the arguments in an EFI Shell to enable one of these card + bridge combinations, I also had to change the graphics adapter in macOS under the "Energy Saver" option!
So, if I wanted to use only the integrated 9400M, I'd first boot into macOS, go to settings, select from Energy Saver "Better battery life", reboot, boot to uEFI shell, pass the arguments (mm 0750 -IO 0, mm 0010003E -PCI 8, mm 03000004 -PCI 7) and I'd be looking at an idle consumption of 27W and a 42-53W consumption while running Heaven benchmark, at full brightness.
Then, if I wanted to run the discrete 9600M GT, I'd pop back into macOS again, select "Better graphical performance", reboot, go to uEFI, type in the 9600M stuff (mm 0750 -IO 3, mm 000C003E -PCI 8, mm 02000004 -PCI 7) and the power draws would be 34W at desktop and between 62-72W running Heaven.
The processor (T9550 in my case) actually started throttling after about 20 minutes with the 9600M GT, locking itself to the lowest 6x multiplier. You can disable this kind of behaviour of course with Throttlestop, but what I ended up doing with it was undervolting the CPU. I also have MSI Afterburner installed, we'll see how much of an improvement overclocking the GPU makes..
I had no other issues with any other drivers with this uEFI installation, I used the latest recommended Boot Camp driver pack (4.0.4033) but for the nVidia drivers I had to manually extract the latest supported package (342.01) and force the "Basic Microsoft Display Adapter" to use the respective drivers by pointing to the extracted .inf files. I couldn't get the installer to run but the .inf files are all that's needed anyways..
Like before, hope this helps again somebody else who is having a hard time!