Before running this, I recommend existing zenoss install to be removed, rm -rf /opt/zenoss, and reinstall it clean.
#!/bin/sh
ZENOSS_DIR="/opt/zenoss"
PYTHON="/usr/bin/python2.4"
cd $ZENOSS_DIR
find . -type f -exec sed -i "s|/usr/bin/python|${ZENOSS_DIR}/bin/python|g" '{}' ';'
cd $ZENOSS_DIR/bin
rm python
ln -s $PYTHON python
A little description about the above script. It simply change all /usr/bin/python to /opt/zenoss/bin/python and replace the symlink /opt/zenoss/bin/python to point to /usr/bin/python2.4
Now Zenoss can be started using /sbin/service zenoss start.
Happy that I have a test instance now, time to figure out how to install it on freebsd qemu. >.<