If you move the viewer out of full-screen mode you can drag its window icon (top left of the titlebar) to photoshop to drop the file into the program.
You can also use Ctrl-T to tag the current file, if the lister you opened the viewer from is still open. Will make it easier to find.
When using the preview panel (not the viewer), you can double-click the image preview to do the same as double-clicking the file (which could open it in Photoshop if that's how double-click is set for the file).
If you want anything else, send a feature request.
BTW, as I feared, this thread has become difficult to follow. This is why we request that people ask one question per post.