Andrew, a charter captain friend of mine has a custom made tool for this very purpose. It is far easier to use than long pliers which I think you will find unwieldy and hard to use while the fish is still in the water. He made the tool for de-hooking deep-hooked GTs, but it works well over the side of the boat also.
It is hard to describe but I will get a photo when I next see him and post here. Any stainless steel worker or someone with basic welding skills could make one.