If destination folder already exists ADD source contents

I am trying to setup a rule to help me manually manage my iTunes folder, and I can't figure out this one part
My iTunes folder is set up like this:
iTunes>Music>(Artists)>(Albums)>(Songs)
Say I download a folder of music by the artist "The National".
My Downloads folder now contains this:
Downloads>The National>Trouble Will Find Me>(songs and album art)
What I can't figure out is how to make Hazel move the folder into the iTunes Music folder particularly if that artist's folder already exists.
If the destination already has a folder of that name ("The National"), how do I get Hazel to ADD the new folder (the new album: "Trouble Will Find Me") to the already existing folder of that artist?
If a folder for that artist doesn't exist yet, obviously create one and keep the "The National>Trouble Will Find Me>(songs and album art)" structure
My iTunes folder is set up like this:
iTunes>Music>(Artists)>(Albums)>(Songs)
Say I download a folder of music by the artist "The National".
My Downloads folder now contains this:
Downloads>The National>Trouble Will Find Me>(songs and album art)
What I can't figure out is how to make Hazel move the folder into the iTunes Music folder particularly if that artist's folder already exists.
If the destination already has a folder of that name ("The National"), how do I get Hazel to ADD the new folder (the new album: "Trouble Will Find Me") to the already existing folder of that artist?
If a folder for that artist doesn't exist yet, obviously create one and keep the "The National>Trouble Will Find Me>(songs and album art)" structure