Bake Nightfall into the class spec "perk". You get it automatically when you spec Affliction and Mastery could increase it's proc rate by a small amount.
Where Nightfall is, put a Talent [insert witty name here]
Your Shadowbolt inflicts the target with [insert witty name here] ,causing 15/30% of it's damage as a Damage Over Time effect over X seconds.
Bake Burning Embers into the class spec "perks". Where Burning embers is located, move Empowered Imp there. Where Empowered Imp is replace it with
Your Empowered Imp procs also cause your next Soulfire cast to increase your spell haste by 15% after you deal damage with Soulfire.