Spear Dancing Reach (Combat)Source Weapon Master's Handbook pg. 17
You can strike from afar with double weapons.
Prerequisites: Dex 17, Spear Dancing Spiral, Spear Dancing Style, Two-Weapon Fighting, Weapon Finesse, Weapon Focus with the chosen weapon.
Benefit: While using Spear Dancing Style and making a full attack using the chosen weapon as a double weapon, you can grant the reach special weapon feature to one or both of the weapon’s ends until the end of your turn as a swift action.