You can actually knock this out right now! Here’s how:
First, go to your address’s DNS page and add an A record for www that points to 5.78.24.5. (You can set the TTL to whatever you like, though maybe go with something lower like 300 while testing this.)
Next, head over to your address’s Switchboard page. Scroll to the bottom and add www.arkhamcookie.omg.lol as an External Domain.
After submitting that, check your external domain routes list — if you see www.arkhamcookie.omg.lol listed as “needing help”, just wait a little bit and refresh the page every now and then. Once the DNS stuff is caught up, that message will vanish and you’ll be able to configure the route.
Finally, set the route to Redirect to a URL and plop in https://arkhamcookie.omg.lol.
Presto, you’ve configured your very own server-side redirect for www to the non-www version of your profile page!
Let me know if you run into any issues with the setup, or if you have any other questions.