Based on the pinout from the manual, the audio cable will look like this:
RJ-45 pin #4 (MIC_GND) →
RJ-45 pin #7 (GND) → 3.5mm TRRS sleeve (GND)
RJ-45 pin #5 (MIC) → 3.5mm TRRS ring 1 (RIG_AFIN)
RJ-45 pin #6 (PTT TNG) → 3.5mm TRRS ring 2 (RIG_PTT)
3.5mm TRS tip (PHONES) → 3.5mm TRRS tip (RIG_AFOUT)
As as starting point for the homebrew cable build you can use one of the existing cables with the headphones tail and just re-crimp the RJ-45 connector.