How does one "cheat" on a nail bed drug test?

I have a friend who is in the midst of an ugly custody battle with her ex husband, he is an avid drug abuser and she plans on bringing this up in court and would like for him to be tested. I know it’s SUPER easy to pass a urine test when your actually positive and I’ve even heard of people fooling a hair follicle test. I’m wondering if cheating a nail bed drug test is possible?... We are trying to find the most accurate/hard to fool test. Any info anyone has on the subject would be great. Thank you ahead of time as I know my fellow jellies are going to be of great help!