So even though the Pepsi/iTunes promotion hasn't officially started, the bottles are already out on the street in some areas (which means New York City should get ours sometime around a week before the contest ends). John Stowe was nice enough to take some pictures of his 20 oz. bottle tonight, showing that the 'tilt-back trick' should still work. Brush those teeth and hit the streets—if the sugar doesn't kill you, the carbonation will (but you'll have lots of DRM-locked music).
Update: Some have asked, saliently, "WTF?" You can't really make out the specifics of the cap when you tip it back, but you can see the general pattern of what's printed, so you can make out the 1 in 3 caps that actually have the Pepsi code printed. If I ever get a picture of a winning cap I'll post it and it'll make more sense.
Update Update: Issac Hawley writes
besides the tip trick, you can also take a small flashlight, put it on top of the bottle, and tip the bottle sideways just a bit, and then look at the reflection in the cola.
This allows you to actually read the code, and works on 20 oz as well as 2 liters... but only on dark sodas. And you need a pretty bright little flashlight. And it's suspicious as hell if you're doing it in the store.