As far as I know there's only two ways to reduce carbonation:
1) Let it out of the bottle.
2) Absorb it into the liquid.
#1 is obviously bad, since if CO2 is leaking out you're probably also letting stuff in, and there's no way to do it in a controlled manner. #2 is fine, but the only way to do it is to get the beer cold and leave it there for a while, CO2 absorption into water is higher at colder temperatures. Also, I'm not sure how much of the extra pressure will leave that way, they might still gush.