It's not really a trick, it's just you have to be making your ADR as early in advance as possible. As you are finding out Chef Mickey's can be hard to reserve.
For comparison, I had my 180 day ADR day yesterday, for dining in September, and CM was the first restaurant on my ADR list. I guess the other "trick" was that I started my ADRs exactly at 6am ET when the online system was refreshed with the data for my first day of arrival.
For what time of year are you trying to reserve? I just took a quick look and I am seeing good dinner times fro CM for the week in September I am traveling.