Do you mean the "base" tag? We already do set that (admittedly, after this happened and because of it).
No, he meant the rel="canonical" links.
Oh, that sounds easy enough to do, we'll implement it right away (it should be live in a few minutes. Thanks for the tip, we didn't know about this duplicate content situation...
EDIT: Added!
This does not work across domains, guys. (Among other reasons, it would turn injection attacks into $X million bugs for some companies.)