Tag Feed: Add Multiple Tags into Single Feed

Unfortunately, the Tag Feed plugin doesn't allow multiple tags to be added together to make a single RSS feed for a global multiuser site.

Could this be added to an update?

For example, if I make two posts, one tagged with "cat" and "happy" and another with "cat" and "sad" – I'd like to create a feed that only pulls posts with "cat" + "happy" ...

...In single sites or Wordpress.com, one only needs to add a + (and) or comma (or) in between terms for two feeds to be pulled at one time, e.g.:
yoursite.com/wp-content/tag-feed.php?tag=cat&happy
or
yoursite.com/wp-content/tag-feed.php?tag=cat,happy

Could I bake cookies for the WPMUDev team to make this happen? I'd like to use it on an academic department's website that needs to aggregate their student's work.

Thanks!
Laura