For now, you can at least do a single build of a single revision:

$ export BUILD=linux-amd64-temp
$ docker run \
     -v $HOME/keys/$BUILD.buildkey:/.gobuildkey \
     gobuilders/linux-x86-base \
     /usr/local/bin/builder -rev=50ac9eded6ad -buildroot=/ -v $BUILD

TODO(bradfitz): automate with CoreOS + GCE, ala:
    https://github.com/bradfitz/camlistore/blob/master/misc/gce/create.go