Create a new IK chain that's just the shoulder and the forearm in the goal. Enable that IK instead of the regular hand IK hands.

The manual covers creating IK chains here: https://www.posersoftware.com/documentation/13/index.htm#t=Poser_Reference_Manual%2FTools%2FEditors%2FCreating_IK_Chains.htm%23h&rhsearch=inverse%20kinematic

It's a drag n' drop operation. Click create chain in the Hierarchy Editor. Then, drag the chain pieces in order from beginning to goal. (Shoulder then forearm)

Another tool that you may find useful is the constraint groups. If you add a constraint to the IK goal you can use multiple constraints and turn them on and off during the animation. This has the affect of being able to change the IK goal in the middle of an animation.

Crash from parenting an IK goal ... that's worrying. If you can reproduce that please file a ticket in support with the steps you used.