Oh! That's tricky! To top it off, the handle is "semi-circular"
If you absolutely must have this handle, it's a good idea to pair 2 of them as a lot of the "surface" of the handle will be lost for the hand at an angle.
I think I wouldn't have taken on this task myself if I had encountered the same problem, but instead tried to find a "bar" type handle to mount instead.
Upload pictures both before, during, and after as this is really interesting.
Now I have solved it. Cut straight and "fold" the handle. Then you need to saw out a wedge with rounded/bowed sides.
Here is the prototype. With a bit of soldering and sanding, it will look nice.