I think you can try something like
Code:
/script UIErrorsFrame:Hide()
/console Sound_EnableSFX 0;
/use 13
/use 14
/script UIErrorsFrame:Clear(); UIErrorsFrame:Show()
/cast Incinerate
/console Sound_EnableSFX 1;
but I agree this doesn't look perfect because it's also disabling other in-game SFX a short period of time.