According to this, anyone can request a product key for the PC version of The Club from the game's official site and they'll be sent one without any proof of purchase. We entered our email address but the key hadn't turned up by the time we pressed "publish", so while his appears to be true we have no idea of knowing. It's this edge of the seat journalism that gets us out of bed in the morning.
Update: Yep, it just turned up. You may want to look into that, Sega.