I use 2 methods:
1) Mix chook pellets with a bit of tuna oil plus finely chopped bait. #The pellets stay solid and I drop a few in the water every 30 secs or a minute. #The advantage is that the pellets sink well.
2) The lazy method is to mix pellets, tuna oil, chopped bait, canned cat food, or whatever else I have with a bit of water in ice-cream containers - about 3/4 full. #Don't use too much water at first and don't completely fill the container. #The chook pellets absorb the water and swell. #Continue to add water a bit at a time until the container is full, then freeze.
I use a fish keeper net to deliver the frozen berley, just remove the lid of the ice-cream container and drop it over the side of the boat. #The berley ice-block gradually thaws and releases the berley.
This method works best in winter. #In the summer, the water in Moreton Bay gets a bit too warm and the ice melts too fast.
These methods work in shallow water fishing where the tide flow isn't too strong. Method 2 might work in deeper water if you have some way to take the ice-block down deeper.
Mike