You can do it a couple ways, it just depends on how many you want to feed at a time. I would take some out, say 50, and put them in a separate container and let those hatch. Put the rest in the fridge for 2 days, then take them out for a day or two and resupply your feeder container when you need to.
My 8 chams would eat 500 flies faster than they could hatch, so I probably wouldn't do the fridge method. But if you buy in bulk, or only have one cham to feed, then you might consider trying to lengthen their hatch rate.
I didn't know the Kammers sold fly food. I just got a recipe from them:
Gut loading:
Since the flies emerge with empty stomachs, you will want to "gut-load" the flies to make them nutritious for your chameleons. You can mix a soft-boiled egg (mashed to a smooth consistency) with a few teaspoons of plain yogurt, baby rice cereal and some honey. Once cooled, take the culture out of the fridge and knock the flies down by tapping the container to one side. Carefully open the lid and smear a generous teaspoon full of fly food to the side of the container. When the flies warm back up to room temperature (within minutes), they will immediately begin feeding on the yogurt mixture. Two to three hours later, they should be ready to feed out. From this point forward, the flies can stay out. You can gut load any remaining flies the next day, by following the same procedure listed above.