During a climb animation, you can move the manual aim cursor with L1 + the analog stick, as well as the strafe buttons. The camera position will be stored even after the climb as long as you're still holding L1. This lets you line up vent shots during a climb -- and even still continue to move your aim after the climb finishes -- instead of having to move the cursor from a standstill, saving a few seconds each time.

Example 1: Example 2: