Is it possible to link faders in soundtrack pro to work inversely to each other?

I'd like to automate/link faders in soundtrack pro to work inversely with each other e.g.: I have two dialogue tracks, one processed to mono and left as stereo. I would like to fade down the mono track at key moments and as I do so have the stereo track fade up at the same time maintaining the same volume. (If this wasn't software it would be easy enough to do with two fingers! ) A seesaw action. Is there any way to link and automate this to happen moving only one fader?