See the detailed instructions for the modification at
DFI Street where the author (in his updated instructions) says:
"Now I can already hear you thinking that you would love to do it but nVidia will change the drivers to block SLI on an Ultra chipset.
That can not happen. By performing the mod on the chipset you are turning the Ultra into an SLI. This is a physical change that no driver in the world can detect. Once you close the contacts on the Ultra chipset it is now an SLI chipset.
There are absolutely no driver issues involved since the chipset will now be as much an SLI as a "factory" SLI chipset."