Out here we don't just have bike to work week - its bike to work month... aka the Group Health Commute Challenge
(yes cycling is pretty big out here)

At my place of work (a hospital, so yes there are a lot of workers) there are more than 40 teams of 4 to 10 people. You are supposed to pledge to ride at least 5 times during the month, but most people do it much more. There's also a relatively friendly, but highly competitive atmosphere about the whole thing within my workplace. I'm a regular bike commuter and so are most of the people on my team, as well as two of us being racers (the other guy is a pro.... as well as team doctor, and also a surgeon.... I don't know where he finds the time...)

As far as how to encourage people who come from fairly far away - multi-modal commutes! My workplace gives *everyone* a 3 county bus pass. They try to make it as easy as possible to not drive... Getting people to try alternate commuting is the hardest part, but often after they've tried they often like. Saving all that money on parking (you have to pay for parking at my place of work - you get paid if you don't park), gas, maintenance and not sitting in traffic while you get exercise has its rewards.