otherwise I’d just tell them “I’m working here now!”

Can be a surprisingly effective tactic sometimes.

Just show up for work, start working. Later, complain to HR that you don’t seem to have gotten your onboarding materials, and your first paycheck is late. With a little luck, the HR person will think you were omitted due to an error in the system and they’ll manually add you. And then, congrats – you’ve got a job!