Two words: Milt Sparks. I use one of their IWB holsters for my widebody 1911. With a little creativity, I can conceal under my normal XL t-shirt. With a compact or subcompact gun, I can cover it with a tight undershirt. If you got creative with a mousegun in one of those holsters, you could conceal in a Speedo.
And the best part: I can go 16 hours with that gigantic .45, driving in a truck, with no discomfort.