Are there any other people where you work that bike to work? You might consider asking your employer to install a rack. They're actually not that expensive for a simple metal one.

Sounds crazy but you won't know til you ask.

Is there a secure "utility" closet at your location? I keep mine in the small closet that holds the curcuit breakers and IT routers. No one ever goes in there and, best of all, the door is locked.