If you drop a frozen chunk on a powerhead it will disperse it as it thaws. You can also thaw the chunk for 5 min in some water and then just drop it all in and it will blow around.
We played with these but our foods are too textured and the proteins keep the food stuck together so it really doesn't escape the small holes in the IM feeder. The feeders may work better for smaller foods, like single ingredient cubes like brine shrimp.
I totally understand your concern, however we have been using Premium Aquatics for nearly ten years for residential order fulfillment. They use a proper foam insulated cooler, ample dry ice and I have never heard of any complaints about the food arriving thawed. That was THE number one concern we had when we began using them for residential delivery and they have exceeded our expectations so far.