I keep RF up the entire time, stop attacking at a double attack, then taunt it back after the tank gets hit by it. For feuds you can either stop attacking and heal yourself or take off RF/salv and dps.
Me and my fellow guildies also did our first attempts on this boss last night with me being the 'main' tank as ret. I found that especially the first few times when I use my normal rotation (without using CD's with RF on), I sometimes get the aggro back from the 'Double Attack' tank even without dpsing the boss so a few times I got killed by the Double Attack.
So I tend to just turn off RF as soon as I have a comfortable thread lead and salv and nuke during feuds and it seemed to work out pretty nice. Any tips are still welcome of course