Following cases are now available:
ButtonCommand=PLAY #SKINSPATH#Beeper\Sounds\beep.wav
ButtonCommand=PLAY "#SKINSPATH#Beeper\Sounds\beep.wav"
ButtonCommand=!execute [PLAY #SKINSPATH#Beeper\Sounds\beep.wav]
ButtonCommand=!execute [PLAY "#SKINSPATH#Beeper\Sounds\beep.wav"]