Story Hierarchy support in Greenhopper

For our product, we need to arrange the backlog as following:

Epic, User stories and sub-user stories.

Currently GH supports only 3 levels of hierarchy - Epic, Story and Tasks. This request is to extend the stories hierarchy for more than 3 levels and table view provding required visualization to view the user-stories and sub-userstories.

Without support for nesting of user stories, it is difficult to use Greenhopper.