Preload when using WPML with different domain per language

I have a page with three languages, using WPML with different domain per language.

If I understand things correctly, then the preload function is based on the site’s sitemap.xml to work properly.

However, when you have different domain per language then you also have different sitemap.xml per language.

This means that only our primary language gets preloaded.

Has anyone managed to figure this out? How can I get preloading to work for all my languages when using different domain per language?

https://ww.wp.xz.cn/plugins/w3-total-cache/