For an example of this, check out the iconic Amiri, IIRC, Amiri is the barbarian, and she uses a large bastard sword at -2, with the EWP proficiency to make it legal.
People used to argue that you didn't need Exotic Proficiency to wield a large-sized Bastard Sword, but after much discussion last year (and a subsequent FAQ ) the understanding is as Durngrun explained above.