I'm indeed working for a sports management company (we're player's agents for European soccer players) and have a business card (plus my name is mentioned on our company website), I guess that should work, too? Or does it have to be a club membership, and if so, would my Borussia Dortmund membership card work?
I'm not expecting any troubles although I've booked two stays in the next weeks which included the "ID required" passage when booking. But better safe than sorry.