Manual configuration, or using iBGP (so you do L3 switching basically), see Project Calico, see what Facebook does (IP-IP encapsulation where the outer header is basically their L2 the switched fabric).
Ugh this term bothers me. Just call it routing! That hails from a day when routers sucked so much wind the marketing team at Cisco had to invent a new term for the stuff that did it fast.
Yes, I'd very much like to see TRILL gaining more widespread usage and attention, but fundamentally it's equivalent to IP-IP encapsulation plus IS-IS for link-state and iBGP for the outer IP layer, just with fancy terminology (RBridges and so on) and standardized administration/operational semantics. (Which is a good thing of course.)