If you didn't need the full functionality of the standalone viewer, just a way to quickly view the current image in a separate window then you could write a script to do this relatively easily. Create a simple dialog with a static label and update the dialog when the file selection changes.
This script, whilst also providing a pile of detail you don't need will give you an idea of what I mean : Photo Exif . As you change the file selection in the Lister it will update to show the new selection.