We are using this plugin to set individual Pages to HTTPS:
WordPress HTTPS (SSL)
It turns out our theme was using a hook to block admin access for unauthenticated users. I added a check for the DOING_AJAX constant to the code and it fixed the redirect.
I was able to paste a unicode encrypted version of the email in the link and text. It works as long as you only save once. Like you said, a menu filter hook would be ideal.
