I'm a fairly average sized guy, at 5'10" and about 185 lbs, and have been able to carry and conceal my Kimber Ultra Carry, Mexican style (waiting on my Brommeland Max-Con V,) with my normal-sized, buttoned up shirt over it. I've found that plaids, dark ones especially, work great for breaking up any sort of an outline. Maybe I'm wrong, but I find printed plaids and other similar patterns a little more fashionable than those Hawaiian rags!
Noone's even noticed the extra "bulge" on my side, so I think that I'm doing a pretty good job. Most people aren't looking anyway, right?