On an account with a dedicated IP and SSL enabled, it seems you can’t view/change/delete existing SSL certificates (or add new ones) if secondary domains are added under the account.
I hope you don’t mind, but what is your exact issue.
If it relates to this post, I suspect it was corrected and you need to goto your primary siteworx account, and top right, it states managing yourdomain,url, you can change this to manage your secondary domain and I believe access SSL, but I have not tried it myself sorry.
If you could update your post after it has been resolved, it may help other users.