I found this recent paper on adhoc-IR from CIKM 2013. I haven’t worked in this area but the results seem promising. Essentially, instead of TF, you store an indegree count. The graph in question is the term co-occurrence graph within a window with the direction indicating word-order. The paper won hon. mention at the CIKM so it is clearly very cool.
(c) Shriphani Palakodety 2013-2016