I did the very same thing at my work around a year or so back, it was great experience for the farm I'm running now.
It's a very good thing you've hid it, and if you haven't already I would not tell your coworkers what exactly it is you are doing. In a year, they may just be jealous haters, saying you've got preferential treatment...
http://i879.photobucket.com/albums/ab357/pontiacg5_2010/1157c52c-25d5-4e00-8c6e-444046d21f86_zps1c23c408.jpg?t=1390763947Here is 1/3 of my farm that I've managed to get deployed so far. My rigs love the environment, it stays a steady 60 degrees or so, and my cards stay around 65-70c at the most.
There are 12 290's, 6 280x, and 6 7950 in this picture. Not shown are 12 more 290s I am "proving out" at home, as well as a few other misc cards.
My net hash rate is ~30M

I am sure this has been asked before, so apologies in advance if it has, where did you get those risers? Stateside? Know of any eu suppliers?