This is how i managed, maybe it is of some help. When i was lined up nicely behind the tanker and at the correct altitude for the boom, i engaged AP. From that point i didn't move the elevator axis of the stick anymore (the plane stayed perfectly level with the tanker). Got closer and the boom connected. From there only tiny aileron movements to stay well in line. And i found i had to be just a little more quick with the throttle to keep the boom connected. It took quite some time before completely filled up, but what seemed impossible, suddenly looked easy when the tanks were almost filled. For me AP is the way to go.