Immigration Drug Test!!!

Ok so my boyfriend is undocumented. He moved to the United States when he was only 2 years old. He was covered by DACA but that has now expired and he is applying for his residency. The only problem is the medical evaluation. They are going to preform a blood drug test. We just found this out. We are pretty heavy smokers. We would smoke weed almost everyday for the past year. He does great in school and has a job. But the truth is we just like to smoke. His test is in 20 days and I honestly don’t think that’s enough time to detox his blood from thc. I’ve done a lot of research and it doesn’t look good. I don’t know what is going to happen if he fails this test. I’m hoping he will be able to detox before then but I don’t know.He is a minor btw (16). I don’t know if that changes anything. Has anyone else been in this situation? Any suggestions to make the detox go faster?