Might be helpful to not give as many sunflower seeds and asking him to give you the block two times before getting the food treat and also to substitute a head and beak rub as a reward rather than a food treat each time. You could also combine tricks by doing something like the tube trick combined with the fetch trick. Like go through the tube pick up the block go back through the tube and give you the block or put it in a little cup or something similar, maybe a jar lid. My suggestion is an attempt to extend the interval between the treats as well as to get him to see the trick as accomplishing something rather than as a useless trick. I know that this type of change can sometimes be very beneficial for the parrot. They like to think that they are accomplishing something. Just a though use it how you will or not, it is up to you.