The product of good parenting, wise decisions, and careful life choices. All of those factor into passing a hair drug test.
Having failed these, it makes sense to me that anything that would fry your hair would also deconstruct the chemical composition of any kind of drugs present. The longer the chemical sits, the deeper it will saturate- and the greater the risk of drying out your hair. For the method to work, it clearly must alter the hair itself.
It might be worth attempting a hair color process (and subsequent removal?) or curling or straightening, or something legitimate to defend what will be an obvious chemical dousing of the hair.
You might have better luck investigating the testing process, what chemicals are used, etcetera, and enriching your hair with another chemical that nullifies the testing agent.
BUT: Definitely quit using drugs, and do a detox before taking a job that requires drug-free workers. Just as the drugs are in your hair, they are in your other cells and fat. When the fat burns, for example, LSD users free for years have had "flashbacks" from the drug re-entering their system. Do a fast, do a detox and burn it out. This will also help you in the long run for other, future jobs or testing.