I had one of these two jumps from my homeworld at a bottleneck, the tactic I used: EMP the world, then warp in my ship-cap-worth of T1, 2, and 3 bombers and move them into a position where they wont get shot at by any of the defences. The superfortress takes about 6 volleys to kill just one tech II bomber, and it has to be fairly close to hit through the bombers shield, so you have plenty of time. When the fortress can be shot without bombers taking fire from anything else, order them to attack. If the planet has much scary stuff on it, EMP it and take out the command station, then run back until you have a clearer system.