In the scene where the Pirate King and Ruth are singing the Paradox song look toward the left. A man with a white shirt runs from behind a pillar. I am pretty sure it is a stage hand.
It could very well be the Pirate King. They're all running in and out of the pillars throughout the chorus, and the Pirate King is wearing a white shirt. Unless he's clearly visible elsewhere in that shot, it's probably him.