Jacob Levy has an update:
Proceeding from the other direction: a search just on Hayek restricted to business, economics, finance, law, linguistics, philosophy, political science, psychology, public policy, and sociology eliminated all the false positives I could find. 9385 . Searching for "milton friedman" in those same disciplines (and as far as I know there's no ambiguity in how to refer to him): 8088.
Now, I don't really think that citation counts are going to do the work Wolfers wants them to do here. But on his terms, Hayek is now out of Larry Summers' company, and into Friedman's.
He also shows that searching for further permutations on Hayek's name, such as adding a space where needed, ups the total number of cites a considerable amount.