At my college, you could make arrangements to rent an entire "room"--in reality, a multi-bedroom apartment--from housing directly. You could then have whoever you wanted living in it, presumably unto not having anyone but yourself, if you could afford it. This included co-ed rooming situations.
Actually, I had a roommate who kind of moved her boyfriend in with us. It's one of the reasons we got housing to make her move out.
"Now everyone was giving her that kind of look UFOlogists get when they suddenly say, 'Hey, if you shade your eyes you can see it is just a flock of geese after all.'"
"You can't erase icing."
"I can't believe it doesn't work! I found it on the internet, man!"