The following is Open Game Content from a 3PP Source
You know how to use your spear as a double weapon
Prerequisite: Sojutsu combat style, base attack bonus +8, Two-weapon Fighting.
Benefit: You can strike with the iron pommel of your spear or polearm, treating the weapon as a double weapon and doing 1d4 + Strength bonus damage. If the weapon is a magic weapon, the magic bonuses are not applied unless the weapon was created as a double weapon.
Normal: Most spears and polearms are not double weapons and cannot be used as such without suffering a -6 penalty to attack and -2 penalty to damage.