Actually, you can use Bluff to gain combat advantage twice per encounter: Once as a feint and once through Create a Diversion to Hide, though you'll still need to pass the stealth roll.
Relevant text from Rules Compendium:
Action: Standard action. A creature can take this action only once per encounter.
This line appears in both the feinting and diversion descriptions under bluff.
As a wrinkle, the Hidden status from a Bluff is precarious at best, likened to hiding behind a guy that's looking for you. This isn't the same as using the Stealth skill to hide, even if it involves a Stealth check. Again from the Rules Compendium:
the creature becomes hidden from that target until the end of the current turn or until immediately after the hidden creature makes an attack.
I'm unsure as to whether you'll need to spend an action point to fit in something useful with the CA that turn or if you can wait until the next turn to commence walloping.