Hi there graeme!
I have choosen a different approach, to do that you have to go to
/opt/bitnami/apps/edx/conf/httpd-lms.conf and change the Require local to Require all granted.
# Disable remote access to Django admin console
Require all granted #change local for all granted
ErrorDocument 403 "For security reasons, this URL is only accessible using localhost (127.0.0.1) as the hostname."
Then you have to restart apache:
sudo /opt/bitnami/ctlscript.sh restart apache
And now you can get into the Django admin console.
Beware that you should keep this open just while you are working on it (obviously, if you are still in development you can keep it open because you going to be get in in a lot).
I hope I could help you.