In "The Bath Item Gift Hypothesis" (S02E11), Penny presented Sheldon with a napkin signed by Leonard Nimoy when she saw him in the Cheesecake Factory. Sheldon was overjoyed to receiving the napkin as a Christmas gift from Penny, and overwhelmed on learning the napkin contained Nimoy's DNA. Sheldon briefly mulled the notion of cloning Nimoy, but Penny declined Sheldon's implicit request for a "healthy ovum". The episode concludes with a Saturnalia miracle, a never-seen-before "Sheldon Hug".
In "The Transporter Malfunction" (S05E20), Nimoy voice acts for a Spock action-figure who convinces Sheldon to use his transporter, and then shuns him for replacing it with Leonard's after he broke his own.