My whispergreen fans are actually very easy to disassemble. All the wiring from the fan to the junction box goes through one or two internal plugs, and then it’s like 2 or 3 screws and the entire body of the fan comes out, leaving the housing in the ceiling.
There are plenty of reasons to not want to pull your working fan apart, but with this one it may actually be easier than you think.
If you can swap a switch, then you can probably also install a relay inside the switch box behind the existing switch (assuming there’s room).
@signbit Which modules (if any) do you have in your WhisperGreen fan? (Humidity sensor, Motion Sensor, Multi-speed module). As I detailed over on the Panasonic thread, the wiring on these can get quite complicated.
If I can find the time I can try hooking up one of my Zephyr switches to one of my WhisperGreen Selects and see if I can reproduce your issue.