Auto links to subsites from "portal" site

Hello all,
I have found a lot of plugins that allow content sharing when using multisite wordpress. I am using my main page as a “portal” site for all my subsites. All the plugins I have looked at and are using so far duplicate the content into the portal site.

What I would really like to do is not copy the content over but automatically create a link to the original post in a subsite on the main portal page. This way there is not duplication of content and the subsites are actually visited when somebody clicks “read more” on the main page.

I hope this makes sense, if not I will try to clarify.
Thanks in advance for any suggestions.