Nice try, though.
It's true that the defense didn't file a pretrial immunity petition based on "stand your ground"; that's why the case even went to trial. But SYG was omnipresent in the trial--the defense's arguments all boiled down to asserting that Zimmerman legitimately feared for his life and thus had a right to "stand his ground".
Stop and think for a moment: If SYG laws relieve people of the obligation to use deadly force only if it cannot be avoided, including by giving ground, then if "stand your ground" didn't apply in this case, then he's guilty: Zimmerman admitted that he did not back away, but admitted instead that he aggressively pursued a confrontation with Martin. Without SYG, he'd be guilty of at least manslaughter, if not second degree murder, because he stood his ground.
So yeah, Zimmerman used the stand your ground defense. His lawyers just didn't do it via a pretrial immunity motion.
That's not the only hair-splitting technicality that helped Zimmerman escape justice. It turns out (as described in an Orlando TV reporter's blog that the trial judge decided to not instruct the jurors about the "first aggressor" exception to the justifiable use of force law. It condenses down to what you think it means: Zimmerman initiated the confrontation with Martin, thus giving up a defense of reasonable use of force. Had the jurors been told about that law, the jurors would have received additional instructions:
Aggressor. § 776.041, Fla. Stat.
(T)he use of deadly force is not justifiable if you find:
(Defendant) initially provoked the use of force against [himself] [herself], unless:
a. The force asserted toward the defendant was so great that [he] [she] reasonably believed that [he] [she] was in imminent danger of death or great bodily harm and had exhausted every reasonable means to escape the danger, other than using deadly force on (assailant).
b. In good faith, the defendant withdrew from physical contact with (assailant) and clearly indicated to(assailant) that [he] [she] wanted to withdraw and stop the use of deadly force, but (assailant) continued or resumed the use of force.
776.041(b) would have hung Zimmerman.
It's true once again: The jury decided who had the best lawyer.