Advice on OBNE Signal Blender mod or possibly alternatives

Hey

So I have a Signal Blender from OBNE which I use to blend/mix a clean channel, an overdriven channel and a channel with effects. Love the pedal for what it does.

But I would like to be able to adjust the output volume on the three channels while playing, using my feet. To fade the channels in and out.

How would I go about adding external expression pedals to the volume pots? Is it at all possible?

If not, are there any alternatives to the Signal Blender that would allow me to adjust the volume with a foot pedal?