Not that perverse. Gentoo/Portage has had support for generating RPM packages for ages. It's just that it usually doesn't.
Simply abstracting the dependencies/names into the right places, changing the tarball to cpio, and instead of padding with metadata, making it into a "proper" rpm or deb.
So, not quite as perverse as you may think, in fact part of the original design of portage/emerge was to allow it ;)