I don't believe that is supported. You can request that feature here: http://www.adobe.com/products/premier...
Just scroll down and click on the "Share an idea" tab and fill out the request.
Here's what is currently supported:
Once you've added a soundtrack, the Soundtrack menu displays the settings.
•Tap Replace to select another audio clip
•Adjust the Volume.
•Enable Auto Mix. Auto Mix causes the soundtrack to play quietly when there is sound in the clip.
•Enable or disable Audio Fade In and Audio Fade Out.
•Tap Delete Soundtrack to remove background audio.
Support Product Manager
Pro Video Applications