Sure. Thanks for the help timethief in any case!
For anyone who's reading:
I had 3 blogs on this account, let's call them good.wordpress.com, bad.wordpress.com and ugly.wordpress.com (the entire point of this exercise was to remove connections between my name and these blogs, so I won't use the actual blog names).
I realised that I had created the bad and ugly blogs prematurely - I actually wanted to have them under different usernames - preferably "bad" and "ugly" (for continuity). The WordPress site didn't allow me to create these usernames - any name that has been used for a blog is barred from being created as a username (even if no-one actually has that username) - presumably to avoid someone else registering the name of your blog as their username.
However, seeing as I myself owned these blog names and wanted to create the usernames associated with them, I contacted support to ask if they could do this, i.e. create a user account "bad" with blog bad.wordpress.com and another user account "ugly" with blog ugly.wordpress.com.
They were happy to help and just required that I send them an different email address to register each new account with. It just took a little while to get this all sorted.
[Posted as per request...]