It's an interesting way to use IK driven objects to handle "dumb" objects, place what I call a "IK Handle" on the object. Would it be great to have a handle on everything to allow IK objects to just grab any object by the handle and manipulate its motion through the already existing IK helper that is driving your skinned object. You could have your characters actually pick up a ball and throw it. Well now you can, for a short time limited offer of $29.99 you can.......
just kidding.
Attached are three screenshots that show the way I animated the arm/blocks scene at the top of the thread. The trick is to make a single bone for your "dumb" objects and position it towards the outer edges of your object and skin it, then make a target helper object for the bone to track. It's important to place the bone on the edge or even outside the object slightly so you will not get any intersections with your IK driven object, like a ball passing through the hand rather than resting on it. The target helper object can then be used to track something else (your IK target) and most importantly tracking can be turned on and off in the modifers tab under IK.
When I first did this I used target helper objects for the cube bones to track just because they are easier to distinguish in a scene full of bones. In a small scene though you would not have to use the target helper objects and just let the cube bone track the IK helper object.
I've also attached the scene file for the arm/cubes for viewing.
I hope this helps everyone, it's not impossible just "tricky".