AFAIK the chip has to be the same for SLI to work... The 192 bit memory interface chip is the GTX 460 v2, a newer version of the original GTX 460... So it probably won't work.
GeForce GTX 460 - Specifications - GeForce
EDIT: Looks like you are SOL...
http://www.google.ca/url?sa=t&rct=j&...vSdVkQ&cad=rja