There's not much the crew can do.
If the aircraft has a digital pressurization controller (most do), there is NOTHING they can do. Nada.
If the aircraft has an older analog controller, they might be able to use a standby mode, which MIGHT reduce the cabin rates a LITTLE. Except that nobody practices using standby mode, an airline may have a policy in place that forbids it, AND if they make a mistake with it they WILL cause themselves & all the pax BIG problems. I'd be VERY hesitant to agree to using the standby mode. Particularly if the individual on the flight wasn't flying due to a greater medical need.
You can always ASK the flightcrew, but the chance that it'll do any good is pretty slim.
BEST thing for the kid is to NOT FLY until his ear is better. Period. Rent or borrow a car, go Amtrack, take a bus, extend the vacation, do whatever, but DO NOT make the kid fly with an ear infection. The damage that can be done is pretty severe and runs way, way beyond discomfort during the flight. Many month to heal, perhaps worse.
If it was my kid, I would not permit him to fly, and I wouldn't budge. I'd drive across the country if that's what it took (including calling in sick to do so), but flying with an ear infection is inviting, no, BEGGING, for disaster.
Don't just talk to the family doc, talk to an AME about the wisdom of letting the kid fly. I wouldn't do it, no way.
Snoopy