Penikett, who has also starred in Battlestar Galactica and Dollhouse, confirmed his involvement via Twitter, according to a Man of Steel Facebook page run by fans. While we couldn't find the tweet in question, we did spot a couple of other references made by Penikett to working on the film. He apparently won't tell who he's playing.
Tahmoh, who has also appeared in DC Comics adaptations Smallville and Human Target, will reportedly play the role of Henry Ackerdson, which is suspiciously similar to the name of Henry Ackerson, a character from the direct-to-video animated film Justice League Doom. In that film, the character turned out to be Metallo and used a Kryptonite bullet to make an attempt on Superman's life.
In a meaningless coincidence, the character of Metallo recently appeared in an Action Comics arc which, when collected into a hardcover, was titled "Superman and the Men of Steel."