Can i give him oversized greatsword with Herolab (of course i can correct it manually)? And i cannot find a feat allowing him to use two handed one hand, if it ever exist.@ mountain, instead of improved unarmed strike give him diehard, he just got flat-footed grapple in on him.
remove clear give him exotic feat Mighty Sword proficiency, and then give him a mighty sword...(this part is optional)
You could certainly justify Gregor being a large creature wielding a large bastard sword in one hand. That ought to do it.