I'm currently working with the Y in my community to better address bike commuters' needs. I haven't been involved for long, but I would suggest gathering as much information as you can so that you're not just asking your company to install lockers, but giving them a breakdown of the financial implications. So, poll your coworkers to find out how many of them already commute or would commute by bike if bike lockers were offered. Also find out how much they would pay per month/year to rent a locker. Then, get some quotes from bike locker companies on how much it would cost to buy and install the number of lockers needed. Identify an area on the premises that could accomodate the bicycles.
You might also see if any grant money is available to help defray the costs, for instance from bikebelongs.org or from your local cycling club. If your company is located near other businesses, schools, etc., see if you could pool your resources to build a central bike storage area that all of you can use. I'm not sure how active your local club is, but I know ours has a board member who focuses on commuting. You might talk to them about what has worked elsewhere in your community in terms of encouraging employers to promote commuting. There may be resources out there, financial and otherwise, that will help make the idea more appealing to your employer.
Good luck!
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher