Often times, I wear my shoulder holster under my dress shirt. Short sleeve, . . . long sleeve, . . . just make sure it is of substantial fabric, . . . and a darker color and/or pattern helps also.
Additionally, . . . I often wear a vest or sweater vest to hide the outline of the leather.
You can also put on a good IWB using a second belt under your shirt and trousers and if you just blouse the bottom of the shirt a little bit, it is very hard to see any outline.
I also have been known to Mexican carry my 1911 inside my dress shirt, cross draw on the outside point of my left hip (9:00) and it is reasonably comfortable.
May God bless,
Dwight