It is possible to create a custom workflow to play a song in a playlist. There are a couple commands you would have to include to get this to work.
The first would be to send a power command to the media service. To include this in a custom workflow, the best way to do this would be to use a Send Service Request command. You can then select the zone you want to power on from the drop down menu. Then under service, you would select the iTunes media stream. Then next to event, select the power on workflow. You can leave the Type blank.
Then, you would need to send a command to have the system select what you want it to play.
To do this, search in automator for the name of the host or the chassis(for the chassis based systems) .On the example below, the name of the chassis is SYS12SE. You want to select the output coming form the chassis that your zone is connected to (the below example is using Audio Zone 1 because the audio connection for the "user zone" zone is connected to the Assigned IO of Audio Zone 1.) Select the Resource of DIGITALAUDIO Source and then under Action, select CommandPlayPlaylist.
You will then get two action arguments, Index and PlaylistName. For Index, you will want to fill in the playlist number of the track you want to play, minus one. So, for example, to play the first song on a playlist, you would put 0 in for Index. To play the second track, you would put in 1, and so on. For Playlist name, you would enter the name of the playlist exactly how it is listed in iTunes (Cap sensitive), it is "test" for this example.
This custom workflow will then send a command to power on the iTunes service and then play a specific song in a specific playlist.