Here's a BookMarklet for setting your UserName cookie. Note: you will need to be viewing a c2.com page in your browser when you run it.
Here's a slightly different version (which prompts for the name):
MicrosoftInternetExplorer allows the above code to be put in a Favorite; for other browsers, such as MozillaFirefox, you may need to copy the code to the browser location box and press Enter.
Firefox will let you drag it to the toolbar if it's presented as a link, but unfortunately we can't seem to do that in WikiWikiWeb. -- MarkAufflick
If you no longer want a username, you should be able to delete the cookie by using an expiry date in the past.