Clark Middleton may have only appeared as eccentric DMV employee Glen Carter in 13 episodes of NBC’s “The Blacklist,” but series creator Jon Bokenkamp says the late actor’s mark on the James Spader drama is “undeniable.” That’s why Friday’s episode of “The Blacklist” will serve as a tribute to Middleton, who died last October at the age of 63, following a battling the West Nile Virus.