SV08.12 "Bullet Proof"
The graphics of the Prometheus Project appeared to show "Lex" in a suit resembling the purple and green power suit of the comics and cartoons. It was only a wire frame representation, but the outline was unmistakable.
And another thing. Since Michael Rosenbaum doesn't want to shave his head for a return appearance as Lex, TPTB could always use something along the lines of the Lex Luthor II storylines from the comics where Lex returned as his "son" complete with a full head of red hair. Now our Lex isn't old enough to have a grown son, but Lionel did have another son -- Lucas. Lex could return as "Lucas." They've never said what happened to him IIRC and Lex could have conveniently left his empire to himself by assuming Lucas' identity. Afterall, one of the last images of the episode was the Planet headline that Lex had been declared dead.
We all know that Lex would never stand still for Tess taking his empire if he able to prevent it. And she did wave the red flag before jamming the signal from her implant.