Parental Controls - Individual App Permissioning?

How do I allow access to an individual app (i.e. Pandora) on my children's ipod touch that has parental controls?

I have two daughters one with parental controls set to Age 4+ and the other set to Age 9+. I want to allow them access to Pandora, but given the app is rated 12+ I am unable to provide them access to this free radio. Pandora app itself has controls to limit my daughters to clean lyrics which I plan on doing, but currently I can't figure out a way to limit my daughters access to age appropriate apps / content using parental controls, but individually permission one app - in this case Pandora.

For the Apple Moderators out there, I do allow them to purchase itunes credits for chores, but their music interests are insatiable so I need another option!

Please help!

Regards,

Bill