This is pretty much what closing is for. Ever notice how you can still comment and edit a question thta's been closed? This is why.
Close it ("Not a real question" fits most of them), leave a comment detailing specifically what's missing, and when the asker edits and responds, re-open.
There is full support in the system for searchingsearching closed questions, and they can be deleted after a period of time if no response is forthcoming.