Mapping fader curve adjustment on S2/S4

Mapping fader curve adjustment on S2/S4

I’m a mapping n00b and am having problems figuring out how to adjust the fader curve via my S2. I’m just looking to have two diff settings (sharp/soft) that I can switch between, via shift + . I have the Traktor Bible and it appears like this is totally possible.
I’ve screwed around with the commands, but nothing happens. Any advice?

Currently you can only set crossfader curve:

Add in > Mixer > X-fader > Curve Adjust

Thanks Stewe