How can I change UIImagePickerController navigation bar font?

I need it to be Helvetica Neue Light. Here is how I create the controller

let picker: UIImagePickerController = UIImagePickerController()
picker.delegate = self
picker.allowsEditing = false
picker.navigationBar.tintColor = UIColor.whiteColor()
picker.sourceType = .PhotoLibrary
picker.navigationController?.navigationBar.tintColor = UIColor.blueColor()

self.presentViewController(picker, animated: true, completion: { _ in })