According to the manual of the 310, you can do a cargo-only flight by following these steps:
“For a cargo flight without passengers, clear all seats then select the baggage areas
where the cargo will be stored; the system will fill them 80-100 percent full. Then,
place the remaining cargo in the seats by selecting each one you intend to fill”
However I tried this by selecting cargo first, then selecting a rear seat I intended to fill with cargo, it instead placed a passenger. If I’m following the instructions correctly, it should have placed cargo in the rear seats. Anyone else got this to work?