I’ve given this some thought, but haven’t tested the MIDI part.  I don’t think you can pull this off on the H9 configuration side.  Mainly because no matter what happens before it, the expression pedal will override the current values (to both pedals) when you sweep it.

Just a thought:  Can you plug both outputs of the dual-EXP into the ES-8, instead of direct in?  Then assign them to two different stompboxes over MIDI, or the control outs?  Differentiate with MIDI Channels, or similar, and keep the switching between them all inside the ES-8?