I'm not sure if this works but you can try :
append this line to the [Actions] part of one of ini files in the launchpad folder
Code:
S M = !lipc-wait-event -s 0 com.lab126.powerd goingToScreenSaver && killall mplayer
then refresh launchpad with [shift shift space]
and execute this via [ shift S M ] whenever you need it to be active.