I bet John Olerud could have done it. He was probably the greatest college baseball player of all time and his stats as both a hitter and pitcher were insane. In his sophomore season he hit something like .464 with an .876 SLG and was 15-0 on the mound with a 2.64 ERA.
He suffered a brain aneurysm shortly after that season but came back and put up good numbers in his junior year and completely skipped the minors after the Jays drafted him. No way the Jays, especially Cito Gaston, would let him try doing both.