Ghost/Lightweight Fast Hands/Scavenger, to get back your tactical. Extreme Condition and either Dexterity or Engineer.
And either a stun nade or a shock charge.
What I normally run though is the same as above, but get rid of scavenger and equip an assault shield to keep your back covered. And equip it to close the gap with someone, then suddenly swap to your knife and gut them.
It doesn't make me unfaithful, unless I'm laying down the cable...
The second was basically the same except I ran with a PDW with laser sight instead of the B23R and one of the shock charges.
My advice is this: Don't just run around with your knife out hoping to chain knife kills together. This rarely happens and you will rage. A lot. Just run with your weapon of choice out and try to flank the enemy. Once you get behind them, close on them and switch to your knife for the backstab. This was the most effective tactic I found while going for gold.
Also, whatever you you, do NOT look at your k/d while going for this. It will make you want to punch babies and kittens.
What? No Weather Dominator? You just expect the weather to dominate itself, huh? That's so unprofessional.