How do I animate MKAnnotationView drop?

I have a custom MKAnnotationView where I set my image myself in viewForAnnotation. How do I animate it's drop like I can with MKPinAnnotationView?

My code is

- (MKAnnotationView *)mapView:(MKMapView *)map viewForAnnotation:(id <MKAnnotation>)annotation
{
    static NSString *AnnotationViewID = @"annotationViewID";

    MKAnnotationView *annotationView = (MKAnnotationView *)[mapView dequeueReusableAnnotationViewWithIdentifier:AnnotationViewID];

    if (annotationView == nil)
    {
        annotationView = [[[MKAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:AnnotationViewID] autorelease];
    }

    annotationView.image = [UIImage imageNamed:@"blah.png"];
    annotationView.annotation = annotation;

    return annotationView;
}

Implement the didAddAnnotationViews delegate method and do the animation yourself:

- (void)mapView:(MKMapView *)mapView 
          didAddAnnotationViews:(NSArray *)annotationViews
{
    for (MKAnnotationView *annView in annotationViews)
    {
        CGRect endFrame = annView.frame;
        annView.frame = CGRectOffset(endFrame, 0, -500);
        [UIView animateWithDuration:0.5 
                animations:^{ annView.frame = endFrame; }];
    }
}