Adding songs to a playlist

[GSOgymrat]

Unless I am missing something, there doesn't appear to be an easy way to add a song to an existing playlist on WP. Any work arounds? Let's say I am listening to a song on Smart DJ and find a song I like. With Spotify I add the song to my "New Tunes" playlist and keep listening. The only thing I know to do with Xbox Music is download the song and hit the heart-shaped "like" button so I can find it later. Any other strategies?