http://en.wikipedia.org/wiki/Vulcan_salute
I think you'd have to scotch tape your ring and pinky fingers together to do it.
I doubt Nimoy did that without help from a roll of scotch tape !
I have no problem getting the two fingers next to the thumb to act in unison and stay together...but no way in hell can I get the 4th and 5th fingers to migrate to their side in a Spock sign....I highly doubt he could do that.....