right now a -cvs ebuild (cvs.eclass) breaks if the computer is offline and ECVS_SERVER!=offline. Could you change this to something like: If cvs-server is not available or you are not online, print a warning/hint and try to build from an old checkout.
This was deemed unneeded in gentoo-dev (cvs ebuilds should be fixed to not override $ECVS_SERVER).