Ok so here is the quick how-to. Get the attached gfxutil and template.plist and copy them to your desktop. Open up terminal and type
You should get something along these lines printed out
Now copy that and open the template.plist and look for the line near the top where you see this example and replace it with what you copied. Scroll down near the bottom of the plist and change this:
to whatever model Geforce card you are using. You can also change the Rom-revision to whatever you like. Once your done making your changes save the file as in.plist.
Go back to terminal you should still be in the desktop directory and type this.
you should now have a new file called out.hex on your desktop. Open this file with whatever editor you like it and it will have your new graphics string. Copy it and open finder and head to /Library/Preferences/SystemConfiguration and open up your com.apple.boot.plist. Under the last string, which is usually the timeout
add a couple new lines as follows
close and save the file. If it doesn't let you save it, save as a copy elsewhere and you can move it back replacing the old one. Make sure to save a backup copy of the original just in case. If you had full QE/CI prior to making these changes, browse over to /system/library/extensions and delete the NVinject/Natit or whatever you were using and reboot. Don't hold me responsible if you break your own install but this does work for some, but not all.