I don't think the feat lets you do that. Just like a medium-sized PC can't wield a Large-sized Earthbreaker using Thunder and Fang, the feat only grants what it states it grants: the ability to use the weapon one-handed (not an inappropriately-sized version two-handed). Likewise I wouldn't think it'd allow a small-sized Dorn-Dergar to be wielded as a light weapon.
The -2 to-hit just makes it all the more worse to even attempt dealing with table variation.
I'm making a Divine Strategist of Yamatsumi, the Mountain Lord, and Clerics don't get Climb as a Class Skill. The only character Traits that do are all Regional, and this character already has a Regional Trait, so On-the-Job Training looks to be my only option.