yep, it's not supported - this has been brought up a few times and there are feature requests in for it (I lodged one back in december 2019).
At the outset Rolf did make it clear that this was not a 1:1 dx7 emulation mode. This is what Rolf said back in May 2020 on the gearspace quantum thread: "Many features of the
DX7
translate well to the kernel osc but not all. We haven't tried to model it, but we found it's fun and useful as a starting point for sound design to load some old syx files."