Uhhh you are suppose to have the navigator do that. Or have the co-pilot take over while you plot the course. When you get close to your target the bombardier takes over control anyway so you have time to plot the return course.
I was once at event where Robert Morgan spoke about his time in the USAAC, and his experience at flight school.
He said that he always got the highest marks in his class, one of the best pilots in his training squad, as far as the actual flying, and was offered any assignment he wanted, and any plane he wanted, and everyone was sure he was going to choose to be a fighter pilot. He said he chose to be a bomber pilot because the one thing he could never do was navigate for himself. If he was away from the rest of the squadron he was lost, but he'd heard the bomber pilots got navigators to tell them where to go, and all he would have to do was fly.