Tip for doing drills without defense: IMAGINE!
If you are working out 1 on 0, you must imagine the defense. Everything you do should be game like. Visualize the defender in front of you, visualize the help defenders, visualize your teammates and the game.
If you are using cones or chairs, use your imagination to turn them into defenders.
Don't work out in an empty gym! Fill it up using your mind. This will result in much greater carry over from drills to games.
Also apply this concept when you are working 2/3/4/5 on 0 at your team practice.