Anima Toughness (3.5e Feat)
From D&D Wiki
 Anima Toughness [Monstrous]
Beings without metabolism are raised or constructed with animating force. This force now can be used to toughen them beyond the durability of their basic undead or construct frames, increasing their hit points.
Benefit: You gain 1/2 your charisma modifier as a bonus to your hit points, as if it were your constitution modifier.
Normal: You do not have any bonus hp due to lack of Con.
Special: This feat does not stack with the ability Unholy Toughness.