The case for thinking seriously about Partial Transfiguration:

1) Partial transfiguration is wordless, but wanded.

2) it's a power Riddle doesn't know as per the prophecy.

3) Harry still holding his wand is a Chekov's Gun for a wanded spell such as transfiguration.

4) Yes, that does seems too obvious, but I don't think Eliezer wants to end the story here so he wouldn't want an extremely subtle puzzle.

5) The only evidence against is that Quirrell might have ripped it from Hermione's mind...but he wouldn't know what to look for, would he? And Dumbledore may well have obliviated it away.

Constraints

1) Only very small amounts of matter can be transfigured

2) The want must not be raised, so Harry must transfigure the ground he's pointing at. No transfiguring people's bodies or anything fancy. The air can also be transfigured.

3) Outright explosives will kill Harry as well, so you can't just make a small patch of antimatter or airborne lethal toxin unless you can find a way to shield Harry.

So, guys - any ideas as to what thimbleful of tiny molecules, placed in the earth a few feet away from Harry, can save him?

EDIT: The case against partial transfiguration as a solution

1) Too obvious

2) Harry holding the wand not Chekov's gun. Riddle is aware that he aught to have disarmed Harry. Not disarming Harry means that somehow Riddle has contingency plans or even actively wants Harry to use the wand.

3) Any combat oriented action almost certainly involves death, regardless of head starts and discreteness, even if we manage to take down Riddle's current body.