The commuting thread is probably best. They are well versed in locking up bikes and being creative.

Is there a parking garage for employees? A parking lot?

You've really explored every option by talking to people?

Scour your building from bottom up and find corners, out of way alcoves, under stairs, anywhere. Then go to the people that be and explain with theft statistics the need for a space. Don't government offices get a kickback for cycle commuters?

The three most important people in any building are:
1. Custodians
2. Maintenance people
3. Security

Talk to them and work something out, doughnuts every other week, case of beer every month. They will find you a space.

What city?