I recently signed up for Citibike and realized there's no simple way of getting directions that takes into account the Citibike station locations.
The approach here breaks down every trip into 3 steps. The first is walking from the starting address to the nearest Citibike station. The second is biking from the start station to the end station. The last is walking from the end station to the destination address.
I got a lot of the code from the way the Citibike site itself generated the map and just plugged it into the Google Maps API to pull the directions. All the code can be found by looking at the source of the page.