Yamaha SY77 split voices: Sustain-pedal to affect only one Element?

As the title says, I am new to the Yamaha SY77, and I'm making a split voice with piano on the left and sax on the right, and I want the sustain footswitch only to affect the piano. (How) can this be done? It was trivial on the DX7 II-D with a Split-mode Performance, but I can't seem to find a setting on the SY77.

Having programmed the DX7 (II) for a long time, and having read the SY77 manual, I had no big trouble finding my way around the 77, but this one baffles me. I would consider it pretty vanilla to be able to sustain piano chords with the left hand and and then play unsustained lead lines with the right.

In most respects, real-time-controller-wise, the DX7 II seemed more flexible, even though undoubtedly the SY's synth engine is much more capable.

(Also posted to reddit, since the community is still a lot larger, but I'm willing to give lemmy a chance ...)