Backstage.com posted a great article with advice on a way to improve your flow of voice over creativity. If you're also an "on camera" actor, you have probably already tried this. Improv classes.
Taking Improv classes help you loosen up and "get off the script". This inevitably leads to more of a natural, believable you, in your theatrical acting or voice acting, since you are not bound by the words.
Take these "loose", free flowing skills into the booth the next time you record. Get playful in your rehearsing your copy. Make choices that you normally wouldn't try and see if it works!