Help setting up realtime controllers to control volume

[staric]

I want to set up Combi programs where I use the four real-time controllers (and maybe even a foot pedal) to separately control the volume of different patches within the Combi. Take, for example, a Combit with 4 patches in it. I would have thought that I could set each of the four controllers to "Volume" and then set each patch so that it only responds to one of the four controllers, but this doesn't work for some reason - moving one of the controllers still changes all the sounds. I can make this work for two sounds (or two sets of sounds) by setting one controller to "Volume" and another controller to "Expression" and then setting the patches so they only respond to the first or second controller, but that's not what I want.

I know I can also use the on-screen mixer to do this, but that is not very practical for making volume adjustments like this on the fly while playing. It would be far easier to be able to turn one of the knob controllers.

Any other ideas??