In the XF86Config file, look for the "Graphics Device Section" and then under that look for this.
Identifier "** NVIDIA (generic) [nv]"
# Insert Clocks lines here if appropriate
Take out the line
or put a # in front of it. That should disable that feature. I say that because mine would not cut off in Gentoo untill I added that line to the XF86Config file. That should work.