ORIGINAL: RCKen
It's "doable" to put the bigger battery for the receiver, but you won't be able to use the charger that comes with the plane. Well, not exactly. You could use it but it would take days to charge the battery.
The included charger outputs 100mA, so he could charge the battery in 24 hours give or take an hour.
The slower charge rate will also prevent damage to the batteries and permit him to leave it hooked up ( if overlooked ) without causing real harm.