Hi Mike,
You can pass client-specific arguments (in the last parameter clientArgs shown below) when registering the callback:
public void RegisterCallback(ServerNotifyDelegate serverDelegate, ClientNotifyDelegate clientDelegate,
Object userToken, params Object[] clientArgs)
These clientArgs are stored with the NotificationSubscriber, which is available to the service. So for that sample, you could do something like this to get the arguments for each subscriber:
foreach (var subscriber in __notificationManager.GetSubscribers(__serviceKey)) {
var args = subscriber.ClientArguments;
}
Hope this helps!