This is the belt that I use when I need one (which seems to be depressingly often) and it's pretty comfortable under a shirt. Really good support too...http://www.roguefitness.com/schiek-3004-power-lifting-belt
I found that if I take enough Tylenol I dont need to wear a belt or wraps.You're good to go bro.
No way that is fitting under a shirt. I'll look into it though, I might just have to be the new gym weirdo, and wear that shit my whole workout.