I want to use SSL for login/admin. However, since I’m using a shared server, my web host only provides a shared SSL. That means instead of https://www.regular-domain.com I have to go to https://servername.webhostname.com/~myusername/, which throws WordPress off since it expects everything to be under the regular domain.
Using shared SSL for login/admin
Try the WP HTTPS plugin, it has a Shared SSL option. Also see discussion here.