Qt3D Manual MipMap generation

[MikkelL]

I am creating an advanced 3D texture with a custom QTextureImageDataGenerator. It works as it should.
For performance optimization I have now started to use MipMaps and have manage to get it working by setting the Texture3D minificaitonFilter to Texture.NearestMipMapNearest and the generateMipMaps to true. I also set the TextureImageData layers to 4. This work, so far so good :)
Now I face the issue that the auto generated MipMaps are not good enough, so I need to generate them manually.
I have not been able to find any documentation for this, but in the QTextureImageData source code I have found that I can add the MipMap data after the original texture data and then it should be able to load it when setLayers specify the number of MipMaps.
Unfortunately the autogenerated mipmaps are still used. I changed the generateMipMaps flag to false in the hope it would stop overriding my mipmaps but with no luck.

Does anyone know how to manually specify mipmaps in Qt3D?

My current version of Qt is 5.12.7.