Installing Gentoo is the answer to very many problems, especially this one--
However, if you are already programmatically syncing your portage tree, do you need anything else other than the rsync?
All straight from the docs:
Your shell script, run via cron:
RSYNC="/usr/bin/rsync"
OPTS="--quiet --recursive --links --perms --times -D --delete --timeout=300"
SRC="rsync://rsync.de.gentoo.org/gentoo-portage"
DST="/space/gentoo/portage/"
echo "Started update at" `date` >> $0.log 2>&1
logger -t rsync "re-rsyncing the gentoo-portage tree"
${RSYNC} ${OPTS} ${SRC} ${DST} >> $0.log 2>&1
In rsyncd.conf:
pid file = /var/run/rsyncd.pid
max connections = 5
use chroot = yes
uid = nobody
gid = nobody
# Optional: restrict access to your Gentoo boxes
hosts allow = 192.168.0.1 192.168.0.2 192.168.1.0/24
hosts deny = *
[gentoo-portage]
path=/space/gentoo/portage
comment=Portage tree
Then start the rsync daemon like rsync --daemon
I haven't tested any of this, but it should get you pretty close... Unless you want to install portage right under a non-gentoo distro?