Cookies are stored on a per host basis, so depending on how smart your browser is, you may be able to log into http://127.0.0.1 as one user and http://localhost. You should be able to have one session for each different name that points at your server. (you'll need to make sure your webserver maps these additional names to the correct vhost too)

Wether your CGI scripts generate urls in a way that will function correctly under this situation is another question.

I generally have 2 or 3 aliases to my hosts as part of the way the network is set up... one by name (nick), one by service (web, cvs etc), one for the literal IP (server22 for 192.168.5.22 when servers only live on 192.168.5)