iTunes supports consuming an ATOM feed to populate descriptions. For the definition see http://itunesconnect.apple.com/docs/NewsstandAtomFeedSpecification.pdf
This feed can be produced directly from the plugin. It requires the following new fields:
- PNG for the iTunes Cover. It must be a PNG and must be at least 1024px on the long side
- Ability to provide a longer description - up to 2000 characters. If this is not supplied, the shorter edition summary will be used (min. 10 characters)
These are available in the Newsstand Content section of the edition admin. You can get to the feed from the Dashboard.
Note: These fields will only appear if the http://wordpress.org/plugins/meta-box/ plugin is enabled.