Can this callback mechanism be generified?

Hello my fellow Java drinkers. I have a generics issue. Would it be 
possible to devise an API, which would allow me to register a callback 
*somewhere* associated with a class. Say I wish to allow a custom 
formatter to be installed:

1  interface Callback
2  {
3      String format(Object object);
4  }
5
6  class Somewhere
7  {
8      Map<Class, Callback> callbacks = new HashMap<Class, Callback>();
9
10     public void installCallback(Class clazz, Callback callback)
11     {
12         callbacks.put(clazz, callback);
13     }
14
15     public void doCallback(Object obj)
16     {
17         Callback callback = callbacks.get( obj.getClass() );
18         if(callback != null)
19             System.out.println( callback.format( obj ) );
20     }
21 }
22
23     somewhereInstance.installCallback( Date.class, new Callback(){
24         public String format(Object obj)
25         {
26             Date date = (Date)obj;
27             return SimpleDateFormat.getInstance().format(date);
28         }
29     });


The code works, but it requires casting as it very much revolves around 
a top-level Object. Is there any way to generify this, particularly the 
callback itself, since the type actually is known (line 23).

Thanks in advance,
Casper