The virtual keyboard thing did not work for me. Then I realised I was accessing our file server third Remote Desktop and directly on the computer. Plugging in a keyboard and mouse to the Server allowed my to turn on JavaScript Apple Events in Safari and set the password.
However, you can't always do this, so the next best thing is use an accessbility scripting feature and have the machine think a user is doing the clicks, allowing you to set the password:
-- The delays can be shorter, coordinates may vary
-- Best way to get the coordinates is with Apple screen capture (command-shift-4) from upper right to lower left
-- if one spends the time, the click events can be converted to Accessibility AppleScript objects by capturing them as variables, or checking the events and using the events instead of the click coordinates
tell application "System Events"
tell application "Safari"
activate
end tell
delay 1
-- click develop menu (make sure its on first)
click at {430, 12}
delay 1
-- click Allow Javascript menu from Apple Events
click at {615, 615}
delay 1
-- Click the Allow Button
click at {1010, 386}
end tell