Allow comment notifications for all portal users

Currently, when using a public portal, public portal users will not receive comment notifications when other public portal users comment on ideas they have created. Notifications will only happen when an administrator comments on an idea, or if a user is a watcher on an internal idea record. It's not feasible to add all customers as Roadmaps users. In order to facilitate discussion among customers, I want to be able to enable portal users to receive a notification any time anyone comments on an idea they have created or commented on.