The S975 does have a setting for Style Touch. But I presume it affects all style channels the same way.

I play Rolands and I've messed around with the Dynamic Arranger. I originally taught myself on organs and have plenty of bad habits! So I probably just press the keys in a lazy way, instead of "striking" them wrists-up the way you would have to on a piano. Bottom line, I don't have the kind of velocity control one needs to make Dynamic Arranger work effectively.

On the BK9 I sometimes use sliders to control Bass, Pad, etc., as the song builds. I've even messed with doubling the bass to a different octave on another style track. I believe this technique could be executed successfully "hands free" with a custom 3-part expression pedal. If you really want or need this functionality, that's the workaround I suggest you pursue.