Blog in a blog

Hello!

I would have tried searching for the answer to my question, but I'm honestly unsure of what search criteria to use.

I am running a WP multisite install with Buddypress. There is of course the main site, which in addition to managing the community, also publishes content & contains advertising. For every subsequent blog/site, I'd like to include the header and footer of the main site. Of course for anything that is hard coded, this is not a problem. The problem I run into comes from the dynamic content, which of course doesn't exist in every new site. And of course it would be laborious to have to recreate this content each time.

How can I tell Blog2 to use content/data from Blog1?

Thanks!
-jennyb