Self built live/rescue image - adding gentoo-kernel?

[Zucca]

I've previously created a script that pretty much automates my custom initramfs cpio creation.
I can use it to create "universal" amd64 initramfs image too. I have a directory where I point emerge to build generic amd64 binaries by using --root option to emerge. It's actually a shell script which sets custom USE, CFLAGS... and so on before running emerge.
Simple.
But when emerging gentoo-kernel (the package) it still pulls config "patches" from my host systems /etc/kernel/config.d.

Do I need to go full manual way with kernel or can I utilize portage for automating kernel creation for my project.
One possibility is to use chrooting or some container. But then there's also catalyst, which I know very little... yet.

What way people here suggest I should go?
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..: Zucca :..