Biily creates a TimeRay that accidentally beams the Firefly ship into his basement. Or back yard. There'd probably be more space there. He and River get to talking super complicated techno-babbly while Captain Hammer and Simon talk through why it's so wrong they wanna sex up their people (Hammer, Billy- villain vs. hero / River, Simon - well, we talked about that :P) Hammer can instigate the conversation ;)

And then Penny comes home, tells them River and Simon have to go home, and Billy TimeRay's them back.

The ship could also almost land on Mal. Or Wash. Wash. Cause the crew wasn't inside at the time... for some reason :P

I can come up with a more... dirty one if you'd like ;)