http://ddowiki.com/page/Treason_(weapon)
Treason as well. Upgraded, it's Armor piercing 15% and carries deception. I know deception and improved deception seem to double up a bit on effect, I wonder if Armor piercing 10% (from Envenomed blade) and Armor Piercing 15% might do something similar?
Also, with rumors about Gianthold going epic soon, and Epic Treason might also fit your bill, while carrying enough differences to complement the Envenomed Blade, Midnight Greetings, or others.
Oh, and to the guys questioning the idea of a DEX rogue... With weapons like Treason and Envenomed Blade, it becomes possible to essentially invest in only two attributes on a character--like a Barbarian with STR and CON--except--in the case of a Rogue, you're now using the same attribute for Attack/Damage/Evasion/Armor Class/a few rogue skills instead of--on a Barbarian--only using STR for Attack/Damage. With a rogue, this might even make for even greater DPS if he can mitigate his aggro because he can get his primary damage producing attribute about as high without a time limit and stack sneak attack damage on with it all while having the possibility of a reasonable defense as well.
Throw crippling strike and opportunist feats in there and you're just raising how fast you can do damage and--on things you're not killing in one or two hits--peeling back enemy's chance to do you damage as well without needing specific weapons to do so.
If he can find a way to throw a high dodge boost in there, a 20% or better blur item, and other "instant, no damage at all, miss chances", he might just have an interesting and very survivable character.
At least until he gets held or otherwise helpless. *grin*