I don't know if I can describe what I'm thinking, but I'll try anyway.
What if you made a box with a hinged pedal in it, and weighted, to rest on the floor to the left of the piano's pedals. The pedal would need to be long enough to create sufficient movement to move the real pedal. Attach a very strong type of thin cord to the pedal so that when you push down on the pedal the cord is pulled down. This next bit is where you may have reservations: You'd have to screw two eyelets into the bottom of the keyboard--one of each side of the piano's pedal unit. The cord from the boxed pedal would run up to the eyelet on the left, across the underside of the keyboard, through the eyelet on the right, and down to the real pedal where it would be attached to the back of the pedal. When you pressed the boxed pedal, the cord--traveling up, across, and down to the real pedal would lift the back of it as if you were pressing your foot on the front of it.
Maybe it's an unrealistic design. It depends on strong cordage and the willingness to screw eyelets into the piano's underside. And, I don't know if you'd be able to get enough power from it to actually lift the back of the real pedal.
Maybe this makes sense, maybe not. I hope so.