I can do it with a Sparks Summer Special, quite a comfy holster, under a T, but it prints a bit when I bend over or something. So, I prefer to put on a loose vest over that to eliminate any possible printing. I don't mess with it in summer or when I'm working, just pocket carry a 9 or a .38. But, it can be done when it's cool enough to wear the vest. In my experience, 85 degrees or cooler I can do that comfortably. 100 degree days, forget it! A very loose Hawaiian style shirt probably would work with a long tail, one size oversize. I ain't got any Hawaiian shirts, but that's a thought. It's somewhat tropical down here by the bay what with all the palm trees about. Wouldn't look too out of place.
But, still, the weight of the gun, the IWB, it's not nearly as easy on the carrier as pocket carry or even a lighter gun IWB. With my little 9mm or my .38, last choice my .380, I need not ever be unarmed. If all I had was a big gun and a Sparks to carry it in, I'd be unarmed a LOT.
I've never tried smart carry, looks a little hard on the family jewels, though, if you wanted to bend over or sit down or something. Might be a little slower on the draw, especially sitting down.