Korg Poly800/EX800 Users

Since there is voltage control available for pitch it is probably even
possible to do some kind of real FM. But since there's only one osc,
it will be self-modulation. And the osc isn't designed for this either
so it will probably result in some kind of wierd sounds. Especially,
since we don't have smooth waveforms like sine waves.

If you take a closer look at the schematics, the pitch-bend output of
the IC8 multiplexer feeds into the oscillator clock control circuit.
This is also where vibrato gets inserted into synthesis.

Maybe it's possible to route bend to filter cutoff via a switch,
allowing joystick control of the filter.