On Godaddy, it creates the subdomain under the "primary" domain or account.
See the other post where I have replied with cPanel description.
This is also valid on goDaddy as in the other post, you mentionned that the master is a subdirectory of your "primary" domain (or account).
The other post is also valid because goDaddy is totally OK with Symbolic Link and MySQL 5.0 and its MySQL user privileges to share the content.
So apply the procedure described in the post
www.jms2win.com/forum/24-joomla-multi-si...fficult-to-configure