I have thought about this before and i'm probly giving away a great idea
Barra fishing has accommodated for this problem a few ways and one of them is a matt, sort of a piece of canvass or other tough material with a rod down each side and a couple of handles. You simply swim the fish onto it and lift, the matt supports the whole weight along the whole fish. Works well for monster impoundment Barra.
The only thing that conserns me is the anal fins on the gt, do they fold flat? If they dont a matt for lifting would cause serious damage. Swimming a 40kg plus GT onto a matt that would be big enough might be a challenge but what about GT fishing isnt a challenge?