csrutil disable
Restart computer
In the terminal, type
sudo open /Applications/TextEdit.app /System/Library/LaunchDaemons/com.apple.ManagedClient.enroll.plist
change
<key>com.apple.ManagedClient.enroll</key>
<true/>
to
<key>com.apple.ManagedClient.enroll</key>
<false/>
So that the changes take effect
Even with a complete wipe of the hard drive and an installer on a USB stick, you can't do an install without being online. I even tried doing a restore from a Time Machine backup and it won't proceed without an online connection.