Reduce the base damage of Mutilate significantly, and slightly reduce the base damage of Envenom and Eviscerate. Then, let Deadly Poison stack to 10 and increase its duration. Continue to allow all moves to scale the way they currently do with stats like Attack Power.
You've buffed overall rogue damage for all three raid specs in raids, while reducing Mutilate's burst damage in PvP only.
Deadly Poison will do more damage, but won't reach its full potential unless the fight is long enough for you to get your stacks up. It lasts longer so you aren't punished for having to move during raid bosses. It also reduces how much of rogue damage is mitigated by armor by making a larger portion of it poison damage.
In PvP, rogues will face a major trade-off if they choose to use Deadly Poison: they get less advantage from Deadly Brew (which procs Crippling off of other poisons besides Deadly), and they can't use Gouge or Blind as freely on a target that has a DoT on them. So you force pvp rogues to pick between either more sustained damage, or more control, while nerfing their burst damage. Their raid damage is still the same because the extra Deadly Poison damage makes up for the nerfs to Mut and Envenom, while raid damage for Combat goes up. HaT builds (deep Subtlety raid builds based off the talent Honor Among Thieves) stay at roughly the same damage as their Deadly dps goes up but their Eviscerates go down a little.
Busy day at work, Dale the Game Mechanic is still on his way.
LATE NIGHT EDIT: I was thinking about this, and just realized that Envenom wipes Deadly Poison stacks, so this wouldn't be very Assassination-friendly. If the damage of Envenom were reduced slightly, could we get away with having it not remove Deadly?