Dunno if you're still interested all this time later, but I get to a piano-related noise situation that I find satisfying and kinda fun! Isn't going to fool anyone, and probably has more in common than an old electric church organ, but it has that snappy, chime-y quality that reminds me of the response from playing a piano (if that makes sense). Anyway, I bet a synthesist with more expertise than I could tweak this into something pretty clean.
enable 4 pole, sync and tune the oscillators exactly, with a touch of slop to keep it interesting. Make sure key amount is at 64, raise resonance all the way up and ear tune the filter cutoff until it's at the octave you like. This will give a good sine wave foundation. Osc 1 & 2 I put on pulse and saw+tri, respectively, and futz with audio mod until I find something that resonates with some sub. Set the mod wheel to env release to fake a piano pedal (or just route a pedal), lowest attack, decay highest, highest sustain, high release (as you like) unless using the mod wheel. Env3 to all osc shapes, find a movement that sounds good to you. Effects on chorus or reverb, whichever you like better. It definitely sounds more convincing at higher octaves.
Lemme know if you try it! I enjoy pretending like I'm good at playing keys with this voice haha (nothing like C and Am!)