Try this:
Climb above a buff, at about a 1,000-1,500 ft advantage. Run parallel with it until you are about his/her 10 or 2 O'clock. Now drift over toward the bomber until about 1.6 away. Dive on them, firing while the bomber is still under your nose. As the bomber returns to view you will see splashes all over the wing and fuselage, and that buff will now be on fire.
By attacking this way you are only in the field of fire of the top gun, but you are going so fast it can't track you. Extend and roll away after the pass, and whatever does manage to hit you will do no harm. You can repeat as often as necessary, but one pass will generally do it.
Watch Wimp in his Nikki; he climbs directly above and drops straight down. It works every time!