Currently HaT combo points aren't removed after switching specs, allowing you to get 5 up from heals before any boss fight/attempt (healers usually heal pre-fight to get up their spirit 4pc set bonuses, etc).
1. Make sure you're Sub spec with Honor Among Thieves while everyone is buffing/healing up before an attempt and be targetting the boss. If you don't get 5CP before it's time to pull, ask for heals before you hit the ready check.
2. Switch to your normal Assassination spec when you get the 5CPs.
3. Have your 2pc T6 equipped (any two pieces) and when it's time to pull, put up a Slice and Dice with the combo points, then switch to your normal gear. (equipment manager makes this easier/faster, just put the gear sets on your bars).
4. The Slice and Dice should keep being refreshed by Cut to the Chase, and stay at 45% instead of 40% like usual.
The old Sub mastery as Assassination bug was fixed by removing SnD + premed points after switching specs, but since HaT points stay, this part is still possible. 5% attack speed is a decent DPS increase especially considering poison procs, but I haven't seen this posted by any other Rogues or known by anyone else besides me and the Rogue I've told before this in guild.