[eecc]

Segmenting the cargo hold? Not necessarily all the way to the bottom, just enough of disrupt superficial sloshing?

[cwkoss]

I wonder if sheets of a cloth-like material could be used in loading similar to Mechanically Stabilized Earth

Practical Engineering has a great video on this simple but pervasive technology. https://www.youtube.com/watch?v=0olpSN6_TCc

[Terr_]

If it's really behaving like a liquid, then you wouldn't want those gaps.