Same content feeds to multiple sites

Hi, I have a wordpress/buddypress multisite setup and firing, I have a main site that they all sit under

site1.com
subsite1.site1.com
subsite2.site1.com
subsite3.site1.com

etc..

I have content being put into site1.com into multiple categories, I also need to display content, depending on the category on the other sites, so it’s not all content, the category depends on the subsite it goes to.

I’ve looked up site wide tags and categories, can’t find an effective way without hacks, I am aware I can RSS them in but ideally I don’t want people to click on the snippet and be brought to site1.com to read it.

Anyone got a solution?

Many thanks