Here is the method I used to learn the alphabet in reverse. Using phoenetics, and a slightly re-adapted alphabet song, I was able to quickly and permanently download this info to my head. I could seriously be out drunk driving, get in a car crash, have amnesia, and still be able to recite the alphabet backwards during a sobriety test.
Most people learned the alphabet initially from the alphabet song. It is broken down into 8 sections. ABCD-EFG-HIJK-LMNOP-QRS-TUV-WX-YZ
Backwards, using the same 4-3-4-5-3-3-2-2 bars, it becomes:
ZYXW – VUT – SRQP – ONMLK – JIH – GFE – DC – BA
zikeswa – vhat – sirquip – onmilk – jih – gufeh – dic – bah
Practice singing that with the same melody as the alphabet song. Sing it once or twice to get a hang for it, then say the phoenetics aloud a couple times, then do the song again. The phoenetics are rather unique, and if you say them in a unique manner each time, you will easily remember them, and in turn, the letters in each bar will be easy for your brain to extrapolate.
What cops are actually looking for is if you are slurring your letters together…
Should help anyway if they happen to ask you to recite the alphabet backwards, because you’ll be more confident knowing you already have it memorized. At least then you won’t have to focus on finding the letters. Nothing will help you if you’re shitfaced out your mind though.