I don't think the 772 has a barrel adjuster built in. (which stinks IMO)
you can get by with an inline adjuster, like one of these handy Ritchey units, which work great for pretty much any cable routing:
http://compare.ebay.com/like/3005019..._lwgsi=y&cbt=y
I guess you could put it right on the derailleur, or run it within reach on the tt, dt, or wherever it's convenient.