I have just added a function that does almost the same. It fades the volume over time. You can read more in the RPi forum or go to my blog and read/get the code there:
cheers cyber7 (aka Aubrey Kloppers; Cape Town; South Africa)
Another sleep mode alternative: use Tasker on an Android phone. 1. set up a toggle pause task ; http-get-post-commands-for-quick-mpd-play-pause-toggle-t788.html 2. create a Tasker task timer widget on the android homescreen. Click the left side of the widget to set time interval. Then click widget each time you want to activate the sleep timer.
Similarly you can make Tasker turn on RuneAudio when your Android alarm clock goes off in the morning. (Look at the alarm events in Tasker for that.)