It takes patience to do it right but you can kill bombers with total immunity to return fire. 'Its like a game of chess' as patches once told me. He was attacking my bombers at the time but he wasnt doing it right. I discovered this after many many months of going at bombers. I prefer not to attack bombers above 14k but I will do it anyway if I can manage to hold an E advantage. If you are way above them you can BNZ like any plane but they can return fire and a good gunner can take any plane down before he finishes one pass. The way to attack them is with a lot of speed from above and in front. I get out in front of them at least 6k and come at them head on but at least 2k above (six thousand feet). Drop your nose so you are attacking in the vertical as you begin the attack. The gunner will be in the upper turret waiting for a good shot. As you cross his centerline (tip to tip) you want to be pulling a lead angle and firing into the cockpit from directly above if you can manage it (shoot #3 first). He will explode if you can manage two hits to the pilot (I have done it with two bullets). If that kind of shot is difficult for you then go for the left hand wing root. The gunner is defeated at this point because the turret cannot translate to the rear quarter before you have made your pass. Avoid the debris and egress to the front of the bombers while avoiding his return fire (usually you can make 800 yards before he changes guns to shoot). Repeat as needed on #2 and primary.
The only solution to this would be for hitech to program the game to allow for two or more gunners in the upper turret on different aircraft in the same formation (it could already allow that Im not sure). I have made this same attack on two formations attempting mutual support. In that case you move the attack slightly to the oblique and shoot two aircraft at once hitting both #3 of pilot 1 and #3 of pilot 2. They will break up the support and seperate after your first good pass.
Okay the secrets out there now. Go have fun.

Sorry for hijack attempt #2...