How to get SecondaryTexture at runtime?

I see this structure here:
https://docs.unity3d.com/2019.1/Documentation/ScriptReference/SecondarySpriteTexture.html

But no idea how I'm supposed to find that information from a Sprite at runtime?

The TextureImporter has references to this structure. But that doesn't help me at runtime

 

I don't think it's possible atm. https://forum.unity.com/threads/exposing-secondary-textures-at-runtime.975774/ I'm asking for a setter. A getter would be nice too.

 

See the answer using reflection
https://forum.unity.com/threads/grab-secondary-textures-from-sprite-variable.951380/