Sure, you could say it, but even if you were a legitimate journalist with a White House press pass it wouldn't do you any good. Using a false alibi would probably antagonize the judge. The prosecutor could add perjury charges.

The First Amendment does not protect journalists who break the law in pursuit of a story. This was affirmed by a federal appeals court a few years ago (i forget the details) when a reporter was arrested for buying child pornography. He claimed constitutional protection because it was research for a story ... and his editors testified at his trial that this was true. The federal appeals court upheld his conviction. It would be exactly the same for a drug offense.

Trampy