You can switch back and forth between blogs on a multisite with switch_to_blog and restore_current_blog.
That should allow you to get anything you’d like and make queries as if you were actually on the other blog.
Check them out:
http://codex.wordpress.org/WPMU_Functions/switch_to_blog
http://codex.wordpress.org/WPMU_Functions/restore_current_blog
We did a lot of this with one of our recent sites.