Shared SSL Question

My site visitors have accounts but don’t need SSL for login (no sensitive data is stored). However, I would like for the site administrator to use SSL, in order to maintain password security and thus prevent hacker access to superuser functionality. My webhost luckily has Shared SSL, so I can access my site on a secure connection through a different URL:

My Site URL (unsecure): http://www.mydomain.com/
Shared SSL Site URL (secure): https://myusername.myhostname.com/

So basically, I want to use the shared SSL url for admin login, and I want to use the normal domain url for general user login.

Has anyone done this, or knows how to do this? Is it even possible? I don’t want to buy a full SSL certificate if it can be avoided. I have googled high and low, tried a plugin, but no luck. :S