Adjust Ability Scores
Home Brewed Rule
You can trade two points from an ability score you don't want to raise your prime requisite by one point. You can perform this trade as many times as you want. You cannot lower your Constitution, or Charisma. You can only raise your character's prime requisite score.

Example: An elf has Intelligence and Strength scores of 12 and a Wisdom of 13. His player wants him to be both stronger and smarter. He drops the Wisdom score by 2, to 11, so 1 point can be added to Strength. Then he drops the Wisdom again, to 9, and adds 1 to Intelligence. The results are Intelligence and Strength scores of 13 and an adjusted Wisdom of 9.

A cleric with Strength and Wisdom of 15 drops the Strength by 6 (to 9) and raises the Wisdom by 3 (to 18).