StableHost offers unlimited additional domains for your account on certain plans, as long as they are your own domains.
Click "Domains" under the "Domains" section.
Click the "Create A New Domain" button.
Enter the domain name to add in the "Domain" text box.
Deselect the "Share document root (/home/username/public_html) with “domain.tld”." option.
Enter the directory where you want the files for this domain to exist.
Click the "Submit" button.
* The Web Hosting Starter and Mini Plans don't not support additional domains.