While I'm still hoping Casio may introduce this feature either through a firmware update or a Chordana app update, I have found a workable solution using the iMIDIPatchbay app on an iPad. By switching the keyboard to Local Control Off and programming the midi parameters for the keyboard sounds into the app, I'm able to layer the sounds and adjust the volume of the layers via the app. You can also layer keyboard sounds with other app sounds like Korg Module and do things like turn off the sustain pedal for the layer sound etc. It's transformed the keyboard for me but I'm a beginner so I'm not sure if it would suit professional gigging etc. I haven't found a way of renaming the layers on the app, which would be really helpful, instead I just save different setups as songs and title them accordingly.