Check it to make sure it works, but make sure you Undo so that it goes back to the right spot. After creating the IK chain,
you can create your Wrist controller; I renamed mine CTRL_Wrist_R.
To create the controller a circle, then rotate it 90 degrees to the right while holding shift, and then select the original and rotate that one 90 degrees again while holding shift to have 3 circles. Then convert a circle to an Editable Spline, and then click on vertex sub-object mode, and then Attach Mult. and click the other 2 circles so you have one circle all together. Next, once you have your controller, you will align its position only to the IK chain, and then you will align its orientation to the Hand_Dummy_R object. Then, select the IK chain and link it to the CTRL_Wrist_R. Then, select the Hand_Dummy_R object and go to Animation -> Constraints -> Orientation Constraint and once the rubberband shows up click on the CTRL_Wrist_R. So pretty much, this is what you should have, and NOW, all you have left is to setup the Double Rotation.
Select both of the forearm bones (LowerArm01 and LowerArm) and select the CTRL_Wrist_R. Then hold down ALT and Right-Click to bring up the Animation Quad menu, and then click on Freeze Rotation.