Well, I got the SLI actually running, but it looks like you get some pretty strange artifacts when you run nvidia-xconfig --sli=auto, so you are warned. I'm not sure what the right approach is here, but the code looks like.
Also if you have two monitors connected, then if you make on them primary, but the "boot time" monitor (which is different) has a different screen size, then you get this bizarre bug when the smaller monitor tries to display with the larger monitors resolution. The drivers are just confused.

nvidia_card_count=\$(lspci | grep "VGA.*NVIDIA" | wc -l)
if (( nvidia_card_count > 1 ))
then
sudo nvidia-xconfig --sli=Auto
fi