MailChimp: How to use conditional logic with RSS feeds

I have searched MailChimp's documentation as well as other sites but cannot seem to figure out how to use both conditional merge tag blocks with |FEED| merge tags.

Basically I am wanting to combine the two in order to include posts from multiple blogs in my e-mail campaign; in particular, I would like to use conditional logic so that any RSS feeds evaluated as "empty" (meaning no new items) receive alternative content that says something along the lines of "no updates available."

I have tried to come up with a few ways of doing this - none have been successful, but here's the type of thing I had in mind:

*|FEEDBLOCK:http://www.mailchimp.com/blog/feed/|**|FEED:TITLE|**|IF:FEED:POSTS[$content=full] != |**|FEED:POSTS[$count=3,$content=titles]|**|ELSE:|*no updates available for this feed*|END:IF|**|END:FEEDBLOCK|*

any help would be appreciated.