[ghost_warlock]

As others have said, you're probably better off going with one class or the other. However, if you're dead-set on going with a hybrid, you might want to consider going with Sorcerer and Executioner Assassin instead of Rogue.

For one, executioner would give you a Dex-based MBA for free. Also, you could MC warlock via pact initiate to pick up an extra encounter attack (probably eyebite) and then grab Cursed Shadow to get the warlock's Shadow Walk feature. It looks like they changed the assassin's extra damage so it only applies to assassin powers now, unfortunately, so no double dipping striker mechanics any longer.