Posting write-only. EDIT I am no longer write-only

Recall Harry's transfiguration power:

Last week, when the graduating Ravenclaws were discussing their N.E.W.T. scores, Harry had overheard that upper-year Transfiguration practice involved several 'shaping exercises' that relied more on control and precise thinking than raw power; and Harry had promptly set out to learn those, whacking himself hard on the forehead for not trying to read all the later-year textbooks earlier. Professor McGonagall had approved Harry doing a shaping exercise that involved controlling the way in which a Transfiguring object approached its final form - for example, Transfiguring a quill so that the shaft grew out first, then the barbs. Harry was doing an analogous exercise with pencils, growing out the lead first, then surrounding it with wood and finally having the eraser form on top. As Harry had suspected, focusing his attention and magic into a particular part of the pencil's ongoing transformation had proven similar to the mental discipline used in partial Transfiguration - which could indeed have been used to fake the same effect, by partially Transfiguring only the outer layers of the object. This way was proving relatively easier, though.

With this Harry can:

• Partially transfigure his leg into a winding worm. With this leg-worm he could:
  • Touch his transfigured self to Voldemort's magic, thereby causing Voldemort to collapse.
  • Seek out the time-turner . Since the leg is part of his body, twising the time turner would make him go back in time. This is a win, if none of the Death Eaters have cast anti time-turner charms, and Voldemort hasn't either. The death eaters haven't had much time and were immediately given orders. It is unclear if Voldemort would cast wards that could interact with Harry.
• Transfigure all of himself into the adult form of Voldemort and give counter orders. "That's Mad-eye Moody, you nitwits!"
• Partially transfigure his nose to cover his mouth, then cast non-wordless spells

Dumbledore can cast the Patronus wordlessly (chapter 57). Maybe Harry can too, and

• will the Patronus to cover his body (as seen in chapter 100)
• will the Patronus to charge Voldemort
• will the Patronus to Hug Voldemort, changing his utility function with the unknown power...of love!

Of course, there are lots of solutions if you allow Harry to have done stuff off-camera. "Cedric, if I don't meet you at 11:59 tonight carrying a mayonnaise-infused gerbil, please use your time turner to cause a paradox". Harry could turn into his hitherto unseen animagus form ETA which might be a peregrine falcon, the fastest of birds.

And the rest of you, you must fire if Harry Potter tries to run, even if it means striking at your fellow Death Eaters.

Useful