Petlibro cat feeder

One of my three cats has been pushing the buttons lock button on the feeder for the past year. It is extremely annoying to hear it all the time repeating buttons locked buttons locked. However, in the past two weeks, he has figured out how to unlock the machine and then push the other button to get a serving of dry food. So now I have no more control on feeding portions for the cats as they all look at him to unlock the machine. Is there a way to completely lock those buttons so they are unable to touch them or be used?