Is there a way to choose k nearest neighbors in scikits to learn with a user-defined distance metric?

I have to use K nearest neighbors for a set of vectors using the cosine similarity metric and some other user-defined metrics. How can I achieve this using scikits? I found sklearn.neighbors.KNeighborsClassifier, but I was not able to determine any version of the user-defined metrics. I am currently using the latest version of scikits learn 0.11.