Exclude Subdirectory Blogs

Hey all,

Hope this is a quick one.
I have a WordPress (4.0) Multisite installation, and Id like to have the main site ssl secured, but not all the subblogs (subdirectory install).

How can I easily do this with this plugin, and if not with this plugin, how can I do this?

Thanks in advance!
Cheers,
Aron

https://www.ads-software.com/plugins/wordpress-https/