… is to not use TabNavigator at all. Use a ViewStack and RadioButtons in an HBox!
I like doing skinning work in Flex but there certainly are a few components that I often times find easier to just re-engineer than skin. Scroll bars and TabNavigators are some examples of such components. I’ve heard skinning these components has gotten much easier in Flex 4, but alas, all my projects are still being developed in Flex 3.5.