I actually tried to tinker with that app to see how it sends the commands to the musicplayer to switch a song etc and use it the same way but didn't have enough skill to get anything out of it.. :S
dbus-send --session --type=method_call --dest=com.jolla.mediaplayer.remotecontrol /com/jolla/mediaplayer/remotecontrol com.jolla.mediaplayer.remotecontrol.Interface.executeCommand string:"next"