Sysex with Generic Remote?

Is there a way of assigning select buttons that only transmit Sysex messages in Generic Remote or even away of converting the sysex to controller and back again?

I have been setting up an old Yamaha 03D mixer to use as a remote control fader bank. I can get all 32 faders to work but great but the last 4 out of the 32 channel on/off buttons use sysex and not controller messages. I wanted to used then as channel select as the 03Ds own channel select isn’t assignable.