Possible Clues:

• Deputy endlessly on his feet?
• Representative - a good man, and popular
• Greenwood's supporting actor, further characterized as 'groom only'
• Substitute with status finally disappearing
• Replace the person, but not at the sit-in?
• Position no good for a locum
• Vocal pieces
• Status detailed for substitute
• Understudy is nearly permanent
• Deputise; sail close to the shore