Considering baggage collection and check in is basically next to each other at the MCY terminal, there probably wouldn't be a need for Bonza to implement a interline model. Just sell combined insurance in case their flights run late to MCY or MEL, thus missing their 'connection' if they chose to buy a xxx-MCY/MEL-xxx trip (which would require passengers collecting the baggage in MEL or MCY then re-checking for their onward flight anyway as part of the ULCC model).