I know that usually, Yom Nicanor is displaced by the Fast of Esther. But in years (such as 2013 / 5773) when the Fast of Esther is displaced due to Shabbat, may Hallel be said on the 13th of Adar, Yom Nicanor?
Although I am not able to give a source, I do have an answer, as follows: The halochah is that saying hallel on a day when there is no minhag to do so is blasphemy. Also, a requirement of hallel is that on that day there was an open miracle (one the defies the normal rules of nature). Therefore, if there is no minhag to say hallel on Yom Nicanor and no open miracle occured on that day, we can safely assume that you cannot say hallel on Yom Nicanor.