Ah, that's saved in a newer version of Construct. I'll make a cap of my own to show you (I don't want to update until I have time to make sure my game project will work the same in the newest version). Hopefully I'll have it ready in the next half hour.
Edit: Here is the example of my method, I'll try it using image points as I think that should work too and upload that here in a bit.
Edit 2: Alright, that was much quicker to make
Although this method has some disadvantages (you can't reposition the arms at runtime, or load custom offsets from files, etc). Still, this one should be much easier to implement if you want the arm rotation to be hard coded.