Note-ons delayed until CC, note-offs as per keyboard

I am looking for a script to delay notes played until receiving a midi control (a button press on my midi pedalboard). The noteoffs would remain as played on the keyboard. It's to be used on Mainstage, sustained chords are played but I'd like another instrument to echo them while the first instrument is still playing (I might use another midi FX to arpeggiate that second instrument). I'd thought of using Delay Notes Until Next Beat script as a starting point but my knowledge of Javascript is very poor. Any thoughts?