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A Belly band or holster shirt might work for you. A holster shirt would allow you the change in the locker room, assuming you duck into a stall to take the gun in and out. 511 tactical has some that seem ok.
The situation you are describing sounds like you need to just violate the company policy. If you ever have to draw your weapon, the company policy will not be your biggest concern. Others here have mentioned a Surefire flashlight. In your situation, I think this could be extremely valuable. If you have a super bright 120 lum light, you can openly carry it and use it as part of your job, but they are great as a defensive tool at night. If you are on your way to your car and see someone approaching you, light them up. This should blind them, screw up their senses, and allow you to access your weapon from a slow draw, high concealment holster. I would also recommend getting a grip laser.
Conceal deep, and go about your job. Good luck.