How do I make Microsoft Sam whisper?

[MKFRLEBLAHBLAHBLAH]

I can't find a way to make Microsoft Sam Whisper. I know it's possible, because some Microsoft Agent characters have MS Sam's voice, in which MASH supports Microsoft Agent and its whisper feature.

[TETYYS]

I'm not sure, maybe it is just an effect of having a slower speech and lower volume? I have looked through Microsoft Speech documentation but haven't found anything