Swift: Subclassing NSNotification

Hello everyone,

Has anyone figured out a way to subclass NSNotification using Swift? I've done this in the past with Objective-C, but haven't figured out how to accomplish this with the rules for initializers in Swift. I realize there are alternatives to subclassing, but I'd really like to figure out how to do this. Here is a simplified version of what I'm attempting to do:

class MyNotification: NSNotification {

    var someCustomData: String = ""

    override var name: String {
        return ""
    }

    override var object: AnyObject? {
        return nil
    }

    override var userInfo: [NSObject: AnyObject]? {
        return nil
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    init(someCustomData: String) {
        // Compiler wants me to call super.init, but this causes
        // issues since NSNotification is a class cluster.
    }

}

If I try calling super.init or using one of the NSNotification initializers when I instantiate an instance of MyNotification, I get this error:

*** initialization method -initWithName:object:userInfo: cannot be sent to an abstract object of class MyNotification: Create a concrete instance!

Is this currently impossible to do with Swift?

Thanks!