I would really recommend against your third use. The first two are valid, although really, there shouldn't be many times that the second case comes into play. Proper energy and CP management should prevent that from happening.
One thing to remember is that as long as you're not capping out on energy, there's no DPS loss in floating a bit of energy. Especially if you see that the 35% mark is coming in soon, start pooling a bit of energy. That way you can start using Backstab immediately, and still save your Cold Blood for Envenom.
Other than that, there really aren't any other valid uses for Cold Blood. It's a minor energy boost, and a guaranteed crit. Just make sure you're tracking your T11 4pc bonus if you have it, since the Deadly Scheme and Cold Blood will both be consumed on your next Envenom.