So here is how I got it to work for our needs...
#!/bin/bash
tmutil setdestination afp://username:password@ipaddress/volumename
tmutil addexclusion -p /Applications
tmutil addexclusion -p /Library
tmutil addexclusion -p /System
tmutil addexclusion -p /Users/localadmin
tmutil addexclusion -p /Users/Shared
tmutil addexclusion -p /Users/template
tmutil addexclusion -p /Users/teacher
tmutil addexclusion -p /Users/student
tmutil addexclusion -p /bin
tmutil addexclusion -p /cores
tmutil addexclusion -p /etc
tmutil addexclusion -p /Network
tmutil addexclusion -p /private
tmutil addexclusion -p /sbin
tmutil addexclusion -p /tmp
tmutil addexclusion -p /usr
tmutil addexclusion -p /var
tmutil enable
exit 0
Gabe Shackney
Princeton Public Schools