there's a big difference between a program, week, and quarterly/bi-monthly event.

perhaps you're being hard on yourself to say "it fell flat on it's face"! try saying, "if at first you don't succeed..."

once you've done some more research about other programs both at workplaces and in your area, also ask your co-workers for their imput. you get interest when people are interested.

the idea of a pledge card is still good, but it might not be realistic to do it several times a year. that might be something to work towards once you have developed more support amongst the staff.

it does sound like the health coordinator could either be a barrier or an ally, so you might want to approach her again and see if you can come to a meeting of the minds: you want to promote cycle-commuting... she has a job to do. perhaps there were issues that caused previous attempts to not work out long-term (so maybe you have to think short term only); it isn't a lifestyle change that happens easily, maybe everyone is waiting for a reason to be motivated, or a lack of facilities like others have mentioned.