There isn't really - the data model in Netbox is quite simplistic.
* An "interface" represents both a physical port, and a L1/L2/L3 interface. You can't have 4 interfaces on 1 port, except as virtual interfaces
* A "cable" has exactly two ends, and each interface can only accept one cable.
* No modelling of SFPs or fibre pairs
I think your only real option, as you say, is to create 4 interfaces and plug four "cables" into them, as if it were four 10G interfaces (which in fact it is; they're aggregated into one port, but they work as four separate interfaces).
If you were using a QSFP to QSFP cable, then another option would be to create 4 virtual interfaces, as if they were vlans. However that won't work for a QSFP to 4 x SFP+ breakout cable.