I have disproportionately narrow shoulders, so I always get bumps from the ends of the hangers in the shoulders of my shirts. Even using fat hangers doesn't solve this problem - it just makes bigger bumps.
But I've finally figured out a quick and easy solution:
While wearing the shirt, wet your hands, and smooth them over your shoulders. This only takes like 10 seconds and smooths the bumps right out. The only negative is your shoulders are damp for a couple of minutes, but if you'd rather have briefly damp shoulders than hanger bumps, this is the solution you need.