Happy Merry-oake

The anchor of your show chooses an unnamed, random Christmas carol.  With the contestant on the phone, two other cast members are played part of the song and must sing the next line (neither cast member know the song being chosen).  Your listener must choose the line of one of the two cast members as being correct or provide one of their own to win.  Thanks to Bud and Broadway, WIL, St. Louis for the inspiration for this idea.