Well, I ordered some maternity tank tops to wear under some of my maternity shirts. I didn't get to try them on so I knew they wouldn't be perfect fits. Well, I like how they fit and I have some room to grow except they are pretty low cut in the front.
I put on my tank and tried pinching up the shoulders. The armholes are big enough that when I raised the shoulders, the arms weren't cutting into my armpits. If you want to do this, make sure you still have room under the arms.