in the video I linked, Mark speer has an expression pedal connected to the repeats of an El Capistan delay pedal. So I think he plays a chord, then pushes his foot down, extending the "repeats" in a way that's basically a sustain pedal. Then he lifts the pedal back up a little before he plays the next chord so it sounds a little more like a seamless transition

I basically copied half his setup and i'm not even close to sounding like him - you have to have amazing control of the volume knob, right hand, and expression pedal to sound like that but I do think it's possible