We don't have any pre-canned examples on how to do this. However you can take a look at the Thumbnail implementation as a potential template for implementing this feature.
In the ./viewer/ directory there are two class that may be of interest. The ThumbnailsPanel.java is a good point of reference for creating a custom PDF view and the PageThumbnailComponent is basically a stripped down page view which would work well for creating the pageView for the preview.
Creating a custom page view is pretty easy as we have a pretty good class hierarchy and some pretty complete base classes. However the API isn't doesn't allow for the registration of a new view, you'll need to modify the viewer RI.
Each of the current view types:
Which all extend AbstractDocumentView implement DocumentView.
Once you've create you new view you can hook it up the DocumetViewControllerImpl method setViewType()