Hmm.. Heres a couple of feats. Though they havn't been tested yet. Feedback would be nice.
Heavy Strike [General]
You deal additional damage to objects, constructs and corporeal undead.
Prerequisites: Str 15, Craft ( any ) 4 ranks
Benefit: If you successfully critical hit a corporeal creature or object that is immune to critical hits, your attack gains a +2 bonus damage.
Demolishing Strike [General]
You deal additional critical and sneak attack damage against objects, constructs and corporeal undead.
Prerequisites: Power Attack, Heavy Strike, Base attack bonus +3
Benefit: Whenever you score a critical hit, or sneak attack against a corporeal creature or object that is immune to critical hits, you may add half your critical damage or sneak attack damage to the attack.
Improved Demolishing Strike [General]
You are trained to deal normal critical and sneak attack damage against objects, constructs and corporeal undead.
Prerequisites: Demolishing Strike
Benefit: You deal your weapons regulare critical and sneak attack damage to undead, even if they are immune to critical hits.
Special: This replaces the half damage gained from Demolishing Strike, and does not stack.