Check out page 39 of the parameter guide under 1-1d Key Zone.
Hold [On, Off]
Hold is like permanently pressing down on the sustain
pedal. In other words, notes continue to sound as if
you were holding down the key ‐ even after you lift
your fingers from the keyboard.
I think this is what you're after.
Latest Set Up: Kronos 61, Casio Privia, Korg TR61, EoWave Ribbon, Roli Rise 48, TEC Breath Controller, StudioLogic MP-117 Bass Pedals, Moog Theremini.
Past Instruments of Construction: Hammond A100 w/Leslie 760, Korg R3, Roland AxSynth, Korg Poly61, Korg M1, Univox MaxiKorg, Korg MS2000, (2) Moog Concertmate MG1, (2) Hammond X5, Rhodes Mark I & 2, Farfisa Compact, Yamaha S08, Casio SK1, Strymon Mobius, Custom Bass Pedals, Burns B3 Theremin.