edit: 115.9 DRP, forgot my curse but had riposte wrong ...
Ok, here is my build, it looks like it could work to me and I think my DPR calcs are valid (someone check those?). I stated the assumptions made, gear is standard lvl 12.
====== Created Using Wizards of the Coast D&D Character Builder ======
Infernal striker, level 12
Githyanki, Warlock, Lyrandar Wind-Rider
Eldritch Blast: Eldritch Blast Constitution
Eldritch Pact: Infernal Pact
Arcane Implement Proficiency: Arcane Implement Proficiency (Dagger)
Arcane Admixture Damage Type: Arcane Admixture Thunder
Arcane Admixture Power: Hellish Rebuke
Background: Heretic (+2 to History)
FINAL ABILITY SCORES
Str 11, Con 22, Dex 14, Int 20, Wis 9, Cha 11.
STARTING ABILITY SCORES
Str 10, Con 17, Dex 13, Int 15, Wis 8, Cha 10.
AC: 25 Fort: 24 Reflex: 24 Will: 20
HP: 89 Surges: 12 Surge Value: 22
Religion +16, Arcana +16, Thievery +13, History +20
Acrobatics +8, Bluff +6, Diplomacy +6, Dungeoneering +5, Endurance +12, Heal +5, Insight +5, Intimidate +6, Nature +5, Perception +5, Stealth +8, Streetwise +6, Athletics +6
Level 1: Mark of Storm
Level 2: Arcane Implement Proficiency
Level 4: Implement Expertise (Light Blade)
Level 6: White Lotus Riposte
Level 8: Improved Initiative (retrained to Arcane Admixture at Level 12)
Level 10: Dual Implement Spellcaster
Level 11: Called Shot
Level 12: White Lotus Master Riposte
Eldritch Blast: Eldritch Blast
Warlock encounter 1: Vampiric Embrace
Warlock daily 1: The Lash's Bite
Warlock utility 2: Fast Hands
Warlock encounter 3: Fiery Bolt
Warlock daily 5: Tyrannical Threat
Warlock utility 6: Dark One's Own Luck
Warlock encounter 7: Howl of Doom
Warlock daily 9: Feast of Souls
Warlock utility 10: Ethereal Sidestep
Catstep Boots (heroic tier), Subtle Dagger +3, Incisive Dagger Dagger +3, Shadow Warlock Leather Armor +2, Cloak of Translocation +2
Assumptions: the character always has concealment from shadow walk (and can teleport 4 meaning it would need consistent dazes or stuns to stop this). It also benefits from prime shot and will get attacked once by the enemy (easily achieved by sitting next to an enemy).
Hellish Rebuke hit bonus:
6(Con)+6(half level)+3(enhancement bonus)+1(Prime Shot)+1(Storm Bonus Adept)+1(Implement Expertise)+2(Combat Advantage)=+20 vs Reflex
Hellish Rebuke damage (1 hit):
D6+6(Con)+3(Enhancement)+3(Offhand enhancement)+6(Storm Bonus Adept)+5(Called shot)+3(Subtle shot)=29.5 damage
Hellish Rebuke critical damage (1 hit):
3D6+6(max D6)+6(Con)+3(Enhancement)+3(Offhand enhancement)+6(Storm Bonus Adept)+5(Called shot)+3(Subtle shot)=42.5 damage
So, Hellish Rebuke vs Reflex 24:
0.05*(Hellish Rebuke crit)*2(trigger secondary damage)=4.25
0.8*(Hellish Rebuke)*2(trigger secondary damage)=47.2
51.45 damage per Hellish Rebuke on average.
In each turn I get 1 Hellish Rebuke (Standard)+6 damage (Riposte)+Hellish Rebuke (Riposte Mastery)
Note that I am counting the trigger on all of these attacks because I can teleport 4 (including 10ft vertical) and take D10/2 damage (no prone due to catstep boots) to trigger Hellish Rebuke. If the enemy decides not to attack me, DPR drops to around 50 but the enemy is left sitting there doing nothing (the rest of the party has no reason to intervene). Note that any enemy attacking multiple times just gets burned.
Please comment and mostly check my DPR calc.