Global content from main site on MU?

I am looking for some conceptual information here. I am setting up a Head Office site with 10 Branch Office sites. Each Branch office will have the same theme, though with some customization. It seems like a Multisite installation makes the most sense for this. (correct?)

What I am wondering about is the best way to give the Head Office site the ability to create “global” content, ie: add a page and it will appear on all sites, as well as any new sites.

I am thinking it would be best to create a plugin that is activated for all sites that then draws content from the main site as a custom post type. Is that how I should do it, or is there a better way? I am not sure at this point if the branches would be allowed to edit their own version of these bits of content.

Any ideas are appreciate.