Adding theme function to list posts from entire network

I would like to add theme function to list posts from entire network and display in homepage content area in a multisite.

I know there are plugins which are used as widget to do this function but only problem would be not able to show as part of home page content area. There are many themes which sets home page content by selecting category in theme option. If we can add an option to select the blog (MU sub-site) then category in the theme option, this will do wonders.

Please help…