On a gentoo machine I have a second ROOT where I want to give a regular user the ability to install packages. I know there is a config option for portage to change the root usr, but since I use the same portage as for my main ROOT I can not use this.
What would be best is to have an option in make.conf, say PORTAGE_SUPERUSER=<username> that defaults to 'root' if not explicitly specified.
You may be interested in http://www.gentoo.org/proj/en/gentoo-alt/prefix/ - Seems like this project aligns with your goals, unpriveledged and offset.
I'm aware of the "Gentoo Prefix" project, but I don't think it would work for me, the ROOT that I want to be managed by a regular user is used for crosscompiling, using crossdev-wrappers.
anywayz, zmedico if you look into this, please also consider the Prefix code, such that we eventually can both share the same code.