I can only say that it's impossible. Achieving this requires both hardware and software support.
The FSK transmission for K5-K6 was also achieved after countless adjustments, and it can now be transmitted.
However, because the receiver itself is not suitable, it cannot be used for long-distance communication.
However, the so-called USB mode on some K5 devices is actually a broadband operation without complete carrier suppression. Using such a device to transmit results in the same effect as using a linear star in FM mode: useless signals occupy most of the spectrum and interfere with others' reception.
Actually, it would be better to use a CW (continuous wave) mode, which only transmits the carrier signal. This at least wouldn't interfere with the spectrum.😂