Expose feed item node fields (url, guid, etc)

The Create Content > Feed Item form doesn't seem to have a field for adding the source link for the feed item, or for attaching it to a feed (feed reference) and I was wondering whether this could be added. Most of my Feeds are being populated manually, but there are definitely some instances where I need to manually add feed items to the system.

I suppose I could add some cck fields and then just treat as any other node type, but since those values already are stored in the db (in different tables) would it be possible/easy to add those fields to the manual node form?

Thanks for any information.