I've used the rig that you mention when I worked as deckie on a boat in Madeira. The only difference was that instead of a Coastlock snap they tend to use a stainless steel shackle to join the short lure leader to the main wind on (I've attached a picture). They don't use livebaits in Madeira preferring to cover more water by fast trolling with lures. I've live baited with big (10 - 15 lb)skipjack tuna in Mauritius and it's a very successful technique. They take blue and black marlin, hammerhead & mako sharks and BIG yellowfin tuna (only the really big ones can eat a bait that big!). I took a 450 lb blue marlin and a 400 lb hammerhead on the same day with livebait.
I haven't fished for the big bluefin before but I'm told that they're very shy of any hardware near to the lure so I think long fluorocarbon leaders may be required.