The init script in the initrd file.
I will do it for Easy 5.6.4.
My nvidia sfs can be installed via SFSget.
/etc/modprobe.d/nvidia.conf is in the sfs file, which will blacklist i915 and nouveau kernel drivers. If I put that check whether nvidia gpu exists, then at bootup if it doesn't exist, then the sfs won't load, hence /etc/modrobe.d/nvidia.conf won't be there either, and i915 driver will load.
You will not have to explicitly blacklist the nouveau driver if you use my nvidia sfs.