Firstly, you would need to save a version of the username in a URL friendly formatting, stripping out invalid characters.
Then you would need to create a modrewrite rule in your .htaccess file that translated that URL to a real page / url passing the username as the URL value for the recordset filter.
I have some examples of this as its something I have done quite a few times, but not on this computer so unless someone else steps in and beats me to it I'll post them tomorrow (its 23:42 here now)
Cheers
Ian