I don't thing you can do that in LB2, you can shoot rockets only if you have a target designated. Correct me, if I am wrong.
You're right, you can't actually manually aim higher in LB2, but there are ways of making the rockets get on target more.
1) Simply line up the I-beam with the target but DO NOT tilt the helicopter to make the symbol solid. Just align with yaw.
2) Do what real Apache pilots do, and take a running dive at the target. When you accelerate to over 100kts, the auto-elevation for the rocket pods locks, so you can tilt the helicopter up/down to aim the rockets higher or lower respectively.