link like this:
ls -s drupaldir subdir

and name your site folder localhost.subdir.
Domain name changes

Once a site is in production in a particular subdirectory under the sites directory, the subdirectory should not be renamed, even if the Web site URL changes. This is because several database tables (for example: system and files) include references to "sites/www.mydomain.com." Instead of renaming the sites directory, you can create a symlink to the new URL from the old one. Navigate to the sites directory and then use the following command:
$ ln -s /path/to/drupal/sites/old.domainname.com new.domainname.com
Security Concerns

You might want to reconsider using Drupal's multi-site configuration, in situations where the administrators for all of the sites being run from the same code base are not either the same person or a small group with a high level of mutual trust. The reason is that anyone with full administrative privileges on a Drupal site can execute arbitrary PHP code on that site through various means (even without FTP access to the site), and that arbitrary PHP code could be used from one site to affect another site, if the two sites are in the same HTTP document root and sharing the same Drupal code.

So, unless you completely trust all of the administrators of the sites you are considering running from the same Drupal code base to be knowledgeable, careful, and not malicious, you might want to consider installing their Drupal sites in completely separate areas of the web server that are not able to affect each o