How to get a sostenuto function to work in Gig Performer 4?

Hi friends,

I am a guitar synth player and I would like to be able to use a sostenuto pedal function instead of a sustain pedal. Meaning I want to play a chord, press the sostenuto pedal so that the notes I initially played will sustain, but that notes played after the pedal is pressed play normally as if no pedal was involved. I see that cc 66 in the MIDI specification is set aside for this function. Thus my expectation would be that it should work as simply as assigning a pedal to cc 64 for sustain does. And yet it doesn’t seem to work.

How can I set this up to work in Gig Performer 4? Any help or tips would be greatly appreciated.

Maybe this can give some ideas: [Gig] Sostenuto and Sustain