How do you pass a blood test for THC?

There is NO possible way of "passing" a blood test if you do not meet the requirements. A blood test is not a 'test' like a math test it is simply a measurement of what is in your blood at any given time. As this is in the "drug test" category I would say that the good guys are keeping up with the bad guys and the only way to 'pass' a blood test is to not take drugs.