That is probably the easiest way. You might be able to position the valve so you could use the existing hoses from the loader valve. Then you would need two short ones to go to the existing curl function hard lines on the load arm and two long ones for your grapple.
Another option would be to mount the valve out on the loader cross member tube. You would have to cap off one side of the hard piping where the curl hoses connect and use the other side to connect to your diverter valve. Then you would have to run new hoses from the valve to the curl cylinders and your grapple.