Well, I actually wanted it myself wink... I've meanwhile also added two tool-buttons (right of the "Clear" button) which replicate the same functionality as "save as" and "use as" in the image-viewer's context-menu for the currently selected thumbnail (a QMenu can gladly be reused as the menu attached to a tool-button, because it doesn't take ownership of the menu object).

A mind is like a parachute. It doesn't work unless it's open. [Frank Zappa]