You can add this overlay using this file for layman : http://gpo.zugaina.org/lst/gpo-repositories.xml
You can use this file by using layman -o http://gpo.zugaina.org/lst/gpo-repositories.xml
You can see ebuilds in this overlay here : http://gpo.zugaina.org/Overlays/bgo-overlay
This dirty page will be updated soon ;)