if [[ "$(who | grep console)" == "" ]]; then # Runs ONLY if no one is logged in
touch /var/db/.AccessibilityAPIEnabled

osascript <<EOT

set username_ to "localadmin"
set password_ to "localpass"

tell application "System Events"
key code 125 -- Down Arrow
key code 125 -- Down Arrow
delay 1
key code 125 -- Down Arrow
key code 125 -- Down Arrow
tell process "SecurityAgent"
set value of text field 1 of window "Login" to password_
set value of text field 2 of window "Login" to username_
delay 0.5
key code 36 -- Return
delay 0.5
key code 36 -- Return
end tell
end tell
EOT
fi

does this mean you found a solution? Because it appears for me that 10.7 is also broke and I cannot get it to work.