I'm trying to keep a set of updated and stable ebuilds for software that is not present in the official Gentoo portage tree or other unofficial overlays.

You can install these by copying them to your local overlay or setting up a new one. Read about that kind of stuff: http://www.gentoo.org/proj/en/overlays/userguide.xml http://learn.clemsonlinux.org/wiki/Gentoo:Overlays