iPhone: force audio output to speaker with headphones plugged in

Question

It seems that the accepted way of doing this is to set the AV category to AVAudioSessionCategoryPlayAndRecord, and then set the property kAudioSessionOverrideAudioRoute_Speaker. I'm using the category AVAudioSessionCategoryPlayback, because it gives me the proper volume with the headphones not plugged in. When I set the category to AVAudioSessionCategoryPlayAndRecord, the audio playback through the speaker with the headphones not plugged in is very soft. I wasn't able to get the desired behavior of playback through the speaker with headphones plugged in with EITHER AV category.

Here's my code with the category set to AVAudioSessionCategoryPlayback:

    AVAudioSession* session = [AVAudioSession sharedInstance];
    NSError* error  = nil;
    BOOL success = [session setActive: YES  error: &error];
    if (success)
        success     = [session setCategory: AVAudioSessionCategoryPlayback  error: &error];

    // To allow ipod music to play
    UInt32 doSetProperty = 1;
    AudioSessionSetProperty (kAudioSessionProperty_OverrideCategoryMixWithOthers, sizeof (doSetProperty), &doSetProperty);

    AudioSessionAddPropertyListener(kAudioSessionProperty_AudioRouteChange,            hardwareRoutePropertyListener,  nil);

    UInt32 audioRouteOverride = kAudioSessionOverrideAudioRoute_Speaker;
    AudioSessionSetProperty(kAudioSessionProperty_OverrideAudioRoute,
                            sizeof (audioRouteOverride),
                            &audioRouteOverride
                            );