How can I add a UITabBarButton with a button that triggers a modal view, rather than just showing one of the tab bar view controller's views? RedLaser accomplishes this. Notice the red "scan" button below. Also, how can I substitute one of the tab bar items with my own image without just slapping an image view over it? The image needs to span the whole area of the bar item.
Instagram also does this with the "Share" button:
Just realized my oversight--simply create a new background image for the tab bar and load that in. On that image, contain any other images that need to go over an entire tab bar item.