Could be a stretch, but maybe someone here knows, because the manual isn't giving me a clear answer...
I've been using a CP300 at my church for a year now and really am happy with the pianos sounds. The pad sounds, however, not so much.
So, my workaround is to bring another keyboard (S90EX) with better pads and MIDI them together. I can use the secondary keyboard for synths sounds by itself and then set the pad patch and layer that over the piano.
What I would really, really like to do is use slider 2 to control MIDI CC#7 to adjust the volume of the keyboard. Right now I can only use slider 1 which also adjusts the volume of the piano part. It's a bummer having to reach up to manually move the volume slider on my other keyboard, as it's a bit of a stretch. I'm thinking maybe with a layer, but I'm not sure how to set it up, and there's nothing in the manual (that I've found) that speaks to using layers for MIDI control.