I think you should just do it without his consent..  And with a disclaimer saying something like "The OFFICIAL ColbertCoin!  Disclaimer: this coin is not endorsed, sanctioned, approved, or condoned by Stephen Colbert, the Colbert Nation, or Viacom.  Any resemblance to any person or fictional character, living or dead, is completely coincidental."  That's what Colbert would do!  Asking permission is a sign of weakness.  Also, on the same day, you should release BearCoin, the greatest threat to the ColbertCoin.