As I recall, its impossible to adjust status to green card from C and D visas. I agree that he needs to consult with an immigration attorney, as the consequences could be quite harsh, if he is accused of misrepresenting his intentions to an immigration officer at the port of entry. On tourist visas attorneys recommend to wait 30-60 days after entry before marriage/employment/study that was not disclosed at the port of entry (google for 30-60 days rule).

And he should not get in touch with immigration agency before talking to an attorney. This agency is there for enforcing immigration laws, not for helping people in questionable situations. There are multiple stories of people getting rolled over for minor immigration violations - i.e. deportation, 10yrs entry ban, etc...