Concealing in the business world has got to be THE SINGLE EASIEST place to do so. Any properly-dressed businessman wears a jacket (yes, even in the office). If you are in a business casual environment, throw a blazer on over jeans. From there, all the way up through suit-and-tie, you can cover any professional occasion and always have a concealed firearm on your belt.
If you simply must insist on walking around the office half-dressed (without a jacket), then use a belly band under a tucked -in shirt.