Creator -Dynamic addition of Customer Portal User Licenses

Creator -Dynamic addition of Customer Portal User Licenses

Hi,

We have a Creator App for B2C about to get released. We are experiencing the Portal User license challenge. Unable to predict the number of users who will download and Subscribe. When a User is about Subscribe and the portal licenses does not exists, it will be a problem. If downloads goes to 20,000 if licenses are not adequate, we will be loosing customers. It is not practical to add portal licenses for huge numbers. Can some dynamic addition of portal user license possible? Is there any similar challenge any one experienced and what is the solution for this?