Maybe you could counter that "If you do it everyone else will...." excuse by pointing out the fact that if everyone else DID bike to work, how much healthier they would be, the less sick leave etc.,etc., etc.

It's tough to change someones mindset, and a lot of managers just take the easy way out, that being "No!". Possibly even going up the ladder to someone higher, tactfully of course, might be the answer.