How to force SSL on all multisite subdomains

I want the admin and specific frontend pages on the main site to be encrypted, but all pages (backend and frontend) on subsites should be encrypted. Wildcard SSL is installed and working. I'm using New Blog Templates for all subsites, with the Wordpress HTTPS plugin activated on the main site and template site (not network activated). This plugin doesn't seem to play well with /wp-signup.php. I can't figure out the right plugin settings and it's not in active development. Wondering if there's a way to implement the desired functionality without the plugin. Any and all help much appreciated.