Yeah, but if there's no way to tell if the phone is jailbroken while it's charging (none that I know of).... if you can't get into the actual system, even if they hook it into a computer at the store... I would guess you'll be greenlighted for a replacement anyway.
you realize that putting a metal object in your microwave will most likely permanently damage your microwave, right? so, you might get a replacement iPhone, but be out a microwave. my microwave cost more than my iPhone, and doing that just doesn't seem like a wise move...
thats sounds by far to risky, i suggest you just over power it! get some rubber gloves, earth your self to something, put to wires into your plug socket and stick 'em into your iPhone! that i believe will kill it!
naturally you may kill yourself but the odds are good, 50/50!
just fry it! no one will ever know, unless you some way melt it! but if your going down the route of breaking microwaves and that, then i suggest you just bite your bottom lip and buy a new one and put your old iPhone back in its box (coffin) and bury it in the back garden with a little cross or something!