not an easy thing...

Basically you need to drop the ability on a ship having low hullpoints left (lower than the overall damage dealt by the current level of that ability), and immediately stop firing on it, and leave the ability to kill the ship, this way it will be yours. But it happened to me many times that the ability stopped right before destroying the ship (thus making it yours). Other times simply my focus fire failed to stop in time.

You need to time it well and let the ability kill that ship, I cannot give you a better hint.