Poser IK definitely has flaws, but I've always found it useful to do animation poses. I can't imagine why it would be useful or necessary to hack a CR2 to disable it (though maybe this is a P5 problem...?). All of my character CR2s have IK off by default so when they're loaded IK is off (I use P4 Pro Pack).

I have pose files in a prominent pose folder which will turn on or off various combinations of hands, feet, or head. So I turn on the IKs when I start the development of the animated pose. Then with IK still on I go to the animation pallette and delete all the keyframes for body parts from the hip (not inclusive) to the IK targets (e.g., hands). This smooths out the body part movements. Then I turn IK off (quickly and easily using my pose files). It's sometimes necessary to turn it back on for, say, the feet to make sure the feet stay firmly planted in the final animated pose, but the end results are almost always quite good.