Screw the thing on, drill a small hole through the brake and into the threads slightly, enough to lock the phanton and barrel together with a pin, and TIG over the top of the pin, all done. You could just send it to somebody that does this everyday, ADCO, Kurt, and countless others could do it for you for a nominal cost.
Whatever you do, do not consider the silver solder idea, something about heating the end of a barrel and muzzle device to a dull cherry red just gives me the "willies".
My 1990 era Bushmaster 11.5-5.5 had 2 pins, and brazed over the top. The 5.5 is no longer on the barrel.
Or do a search for "permanently attaching muzzle device".