What's the best way to have a Target Recommendations Criteria Chain fail cleanly from one criteria to the next?

I'm trying to serve "Recently Viewed Items"  but I want the experience to cleanly fail over to Site Wide Top Sellers if there isn't any recently viewed items data for the visitor. If I build a regular criteria chain it'll populate the first items from Recently Viewed and then backfill the remainder of the set with Top Sellers. Not looking for that, need it to serve one or the other.

Potential (not great) solutions I'm considering;

• Call them both separately hidden, test if Recently Viewed populated and reveal it with JavaScript. It's inelegant and adds unnecessary content to the page but would work.
• Set a user.param on product view and then test for it with a profile script. Would also likely work but this feels like I'm re-building something that already exists and I'm worried the expiration on the param wouldn't match up with the internal expiration on Recently Viewed maybe?

I'm hoping there's something simpler I'm overlooking, if not then I'll use one of the above ideas (and complain about it). Any suggestions are appreciated.

-- Nick