Progressive License is a clever little WordPress plugin that allows the user to, among other things, change the licensing terms for blog posts over time. For example, you could have a copyright notice appear on a blog post until 30 days after it is published whereupon the license automatically switches over to a Creative Commons noncommercial license. If you wanted, you could go further and remove the noncommercial stipulation after, say, 6 months or whatever else you find appropriate.