Another solution (which is a hack) is to set the alpha on the tabBarController to 0.01 so that it is virtually invisible yet still clickable. Then set a an ImageView control on the bottom of the MainWindow nib with your custom tabbar image underneath the alpha'ed tabBarCOntroller. Then swap the images, change colors or hightlight when the tabbarcontroller switches views.
However, you lose the '...more' and customize functionality.