Buy a Fashion Fit Clip from your local fabric store.
Sew on a variety of buttons (I had these already).
Clip on the back of your shirt
That's it! (I know, almost not worth posting)
After I already made the fit clip with a purchased fashion fit clip, I found these curtain rod clips (not in use)
I'm thinking I'm going to try making some shirt fit clips with these clips. Wish me creative luck :)