Q. Can someone give a hand salute with fingers spread like the cohanim do when they say bircas cohanim? (as Nimoy and the Vulcans )?

A. Since the Torah directed the Cohanim to be the ones to bless the Jewish nation, a non-Cohen is forbidden to join other Cohanim for the recitation (Shulchan Aruch O.H. 128: 1 Remoh, Mishna Berura, and Biur Halacha ibid.) The prohibition stands only when it is done in a similar fashion to the Cohanim’s blessing (See Piskey Teshuvot ibid.) It is a widespread popular belief that a non-Cohen should not spread the fingers of his hand in the same manner as the Cohanim do when they recite the blessing of Cohanim, (in the form of the letter Shin.) A source for this tradition is to be found in Rivavos Efraim (O.H. 1: 93) quoting the Zohar.
Horav Shlomo Miller’s Shlit”a opinion is that if it is done only with one hand it is permitted.

Rabbi A. Bartfeld as advised by Horav Shlomo Miller Shlit”a