The test is looking for molecules of the drug deposited in the hair follicles when being consumed - i would suggest that is unlikely you will be able to wash these away, if you damage the hair on your head (with chemical cleaners etc) to such an extent that it is obvious you are trying to get round the test they will take hair from some another region of your body.
It is my understanding that these tests are very accurate where drugs have been used over a long term so I think it is unlikely you will pass. Let us know how you get on though
All the best
Iggy



