Volume for different apps

[necigrad]

I finally got ambitious enough to set up a dock in my car for my iPhone 4S. One of the things I've noticed is that my Navigon volume seems louder then my Pandora volume. I'm speaking in general, not about when Navigon reduces the Pandora volume for a message. Is there some way to control an apps volume individually? Permanently? I'm thinking something like an option in the settings for each app where you can +1, +2, -1, -2 from the base volume or something. Ideally I'd like Pandora to be louder overall, yet still be reduced or muted for the Navigon announcements.