If you can fetch the rootfs.tar.xz manually, you should be able to install/create lxc from it locally. Does that works? You need to create config and use correct template (you should have them already present on your system) and that roofs image. Personally i did not try full manual lxc-create, so i am not sure if you can just grab that rootfs or you have to create meta.tar.xz using that image builder.
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