create a mutator zone that when the player enters it, it changes their class.
then create a class identical to your default class, but uncheck the ability for players to drop items.
if your default player class is 1, and the class where dropping items is disabled is class 2, then when entering the mutator zone set it to change the players class to 2, and when leaving the zone make it change the class back to 1.
hope this makes sense and helps