Jon -
I've done 6 butts on my WSM before (all around the same size as yours). They touch quite a bit at first, but after a few hours, they shrink and are fine. It does take a bit longer... as others have said, count on a few extra hours. But it isn't a huge difference. Once the butts have shrunken down, it is essentially the same as any other cook. Just start with a few more lit briquettes than usual and it gets to temp about as quickly too.
Ditto what paul said about using hot water.
Try it out once with 6 and see how it goes. If you don't like the results, then you can migrate to a second smoker!