My first thought long ago was Arne Darvin, as the character was originally to be played by Benicio del Toro, who already looks like a TOS Klingon with no makeup or wigs needed. The shot of Cumberbatch lifting Spock and JJ's anger at its reveal made me think that he was definitely a Klingon in disguise and his non-human nature was to be a surprise.
My second choice has been Garth for a long time. Just look at Cucumberpatch. He has an angular face like the original Garth. Does he seem too young? Remember that Garth received extensive reconstruction or something like that from the aliens.