The standard method for a rifle with fixed hinge-pin is to tig-weld and re-face the hook. Plenty of patience and lamp-black is required! Even chopper-lump barrels have been done this way, by relieving the brazing somewhat before welding. These days, the metal spraying techniques are gaining wide acceptance, but cannot be done at home.

I have only welded the hooks on SxS shotguns myself, 2 Cashmore sidelocks and a Boswell boxlock, but I wouldn't hesitate to do a double rifle if required. All it needs is care.