Multisites posts hierarchy for built a WP Portal

Hi guys,
I would like to built a network portal like Yahoo. In particular in my multisite configuration the first site level ( and other 3 sites (, and under it. I want to show all recent posts inserted into second level website on homepage. I have tried Post Indexer and Recent Global Posts Widget plugin, but for display all network's posts I need to use it. Is possible include this feature on all WP Loops?

For understand my problem try to visit Yahoo network.

Thank you so much
Best Regards