This sounds really dumb but if you use The specialist set of kill streaks and only select one perk, every time you get that first perk and the kills after you get a specialist bonus! You can also use hardline as a main kill streak and every kill is a bonus!
except you have to die each time because the specialist package does not keep giving you the perks once have unlocked them (when you unlock the one you chose it doesnt keep giving it to you)
Edit: i see what you mean about the bonus but the thing about hardline wouldn't matter except every time you died it would be one kill