I figured out a way to do this. Here is what I did:
For my first attempt I created a new view controller called AdBannerController. For its view I created a full-screen view and two subviews. The first subview (contentView) is for regular content, the second is the AdBannerView. I used an instance of this view controller as the view controller associated with the app window ( [window addSubview: adBannerController.view] ). Then I added my UINavigationController.view as a subview of adBannerController.view: [adBannerController.contentView addSubview: navigationController.view].
This mostly worked except that viewcontrollers pushed to the UINavigationController never got their will/did-load/unload methods called. Shucks. I read in a few places that this is a symptom of the UINavigationController view not being a direct descendant of the app window.
For my second attempt I took the same AdBannerController and derived it from UINavigationController. This time, I did the following in loadView:
- (void)loadView
{
[super loadView];
_contentView = [self.view retain];
self.view = [[[UIView alloc] initWithFrame: _contentView.frame] autorelease];
[self.view addSubview: _contentView];
_adView = [[ADBannerView alloc] initWithFrame: CGRectMake(0, _contentView.bounds.size.height, 320, 50)];
_adView.currentContentSizeIdentifier = ADBannerContentSizeIdentifier320x50;
_adView.delegate = self;
[self.view addSubview: _adView];
/* for visual debugging of view layout
[[_mainView layer] setCornerRadius: 6.0];
[[_mainView layer] setMasksToBounds: YES];
[[_mainView layer] setBorderWidth: 1.5];
[[_mainView layer] setBorderColor: [[UIColor grayColor] CGColor]];
*/
}
Notice what happens - I let the superclass UINavigationController construct its regular "content" view, but I swap it out and replace it with my own view which is a container for both the content and ad views.
This works pretty well. I'm also using three20 and there were a few things required to make this work with that setup, but not too bad.
I hope this helps someone!