you can manage multiple wordpress.com blogs with one username.
create name1.wordpress.com, name2.wordpress.com, name3.wordpress.com each with different email addresses.
then go to name2.wordpress.com and go to add user screen. add name1 as an admin to name2.wordpress.com
then go to name3.wordpress.com and go to add user screen. add name1 as an admin to name3.wordpress.com
now go to wordpress.com and login with name1, you will see links to all the three wordpress.com blogs that you created.