Given the proper thickness shim, I think I can center square stock in a 3 jaw chuck. I just tried it in my shop. I haven’t derived the equation relating stock size to shim thickness but I’m sure Marv can do it quicker. With one jaw vertical, shim goes on it. Other two jaws press on the stock at the top corners.

My chuck jaws have a taper on the flank so that complicates the math.