And for what it's worth, I have been testing - and liking - Duress in my sideboard against Control decks or other archetypes ideally packing Surgical Extraction or Show and Tell. It's completely unexpected and decreases the amount of variance associated with Cabal Therapy "guesses."

Thoughtseize is also fine and probably better because it can bin a dredger in your hand. However, the decks that you'd typically board that kind of protection in against deal damage in the form of Bolt and such that two life is actually quite important if your hand is a bit slower. Either way, no one sees it coming which is why it gets even better when opponents side out their Forces (and it happens) on the play game two.

So far I'm liking it.

My list currently looks like this:

// Lands
4 [AN] City of Brass
4 [TSB] Gemstone Mine
4 [OD] Cephalid Coliseum
1 [VI] Undiscovered Paradise

// Creatures
3 [TO] Ichorid
3 [TO] Putrid Imp
4 [RAV] Stinkweed Imp
4 [RAV] Golgari Grave-Troll
4 [FUT] Narcomoeba
3 [RAV] Golgari Thug
1 [AVR] Griselbrand
1 [RAV] Flame-Kin Zealot

// Spells
2 [TSP] Dread Return
4 [FUT] Bridge from Below
3 [JU] Cabal Therapy
4 [OD] Careful Study
4 [MI] Lion's Eye Diamond
4 [DKA] Faithless Looting
3 [TO] Breakthrough

// Sideboard
SB: 1 [VI] Undiscovered Paradise
SB: 3 [WWK] Nature's Claim
SB: 3 [WL] Firestorm
SB: 2 [TSP] Ancient Grudge
SB: 3 [7E] Duress
SB: 3 [NPH] Surgical Extraction