Logically, the "Called Shot" should already be covered by the Improved Precise Shot feat.
IPS enables you to ignore _anything but total cover_. So, taking it to the extreme, even if your target just sticks his little finger out from behind a wall, you would be entitled to shoot that finger with a regular Ranged Attack Roll with no penalty whatsoever (except for distance).
So consequently, if there is any unarmoured body part, IPS also entitles you to shoot that vulnerable part AT NO PENALTY.
Yeah, it's pretty much broken. So in my games I have rewritten IPS. It lets you ignore up to +4 Cover bonus and gives you a proper Ranged Finesse, in the sense that if your attack roll beats the defenders Dodge+DR, you bypass the armour.