He should be able to take Weapon Focus, Greater WF, Weapon Specialization, Greater WS. Too bad he's not smart enough for Combat Expertise until after you apply the template, or he could get the Whirlwind Attack chain. Power Attack, Cleave, Great Cleave, Improved Bull Rush, Improved Overrun, Improved Sunder could all or separately work. Or maybe the 2-weapon tree. Could even see archery feats, but that's a waste of that great Str.
Anyway, we need a vision for him. I definitely say go with the GWS tree, but that still leaves 10 feats!