From what I understand, what you are trying to do is very hard to achieve. The reason is that the drop is handled not by the application where the drag originates but by the application where the object is dropped - in your case the desktop. There probably is some platform dependent API that is able to perform what you want, but currently Qt won't handle such cases just by itself. You could register a quasi application handling some mime-type in your system and then this application could do "something" to spawn that window, but in my opinion this is a very complex task.
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