Here you go.
/jsonrpc?request={%22jsonrpc%22:%222.0%22,%22id%22:1,%22method%22:%22Player.Open%22,%22params%22:{%22item%22:{%22file%22:%22special://profile/playlists/music/Test.xsp%22},%22options%22:{%22repeat%22:%22all%22}}}
You'll have to create a Smart Playlist first. http://kodi.wiki/view/Smart_playlists Mine was named test. The good news is it will continue to play even with play next turned off.
Next you may need a Stop NR when you are done listening.
/jsonrpc?request={"jsonrpc": "2.0", "method": "Player.Stop", "params": { "playerid": 1 }, "id": 1}