I have an AppleScript (saved as an application) that runs each time the xserve starts. In that AppleScript I have this code:
do shell script "echo `cat /etc/security/admin_password` | sudo -S route -nq add 192.168.10.0/24 192.168.0.1"
It works for me. (I know, this is a convoluted way to do this, but I could not figure out what I was doing wrong with launchd and I already had this mechanism in place, so I did it the wrong way.)