You'd be clearer in your meaning if you wrote a little more clearly what you want.
JFileChooser is a compound component that contains lots of other things. Generally, it's not simple to add things except through the API methods, which is not what you want here (apparently), so it would take some digging through the contents of the chooser's main panel to find where to add what you want. But that requires assumptions that the JFileChooser's implementation doesn't change between Java versions.