Atlantis actor David Hewlett (McKay) made an independent film over the season hiatus with his sister Kate, who will be guesting as Rodney's sister this season. Not only that, but he got Chris Judge (Teal'c), Paul McGillion (Beckett) and Rachel Lutrell (Teyla) to join in - and as the clip shows, it seems they snuck onto the Stargate sets and shot footage in the Daedalus/Odyssey corridors...
Here's the Gateworld article on the movie, from January of this year: