Of all the suggestions made so far in this thread, I like this one the most. I would also combine this suggestion with "progressive practice."
Start out with an easy break shot and after you make it, increase the difficulty by setting up a slightly more difficult angle. As your shot-making improves, you can increase the distance from the object ball and/or apply inside/outside English on the cue ball.
If you miss a shot, then either repeat the shot or make it slightly easier until you can make it consistently.
I definately agree with the "progressive practice" which you describe. However, I feel that the rack must be present because the crux of the problem for me is not just making the shot, but getting an effective break. I do feel that my problem is that my attention is distracted by the pack, along the lines of what Sean mentioned in his post earlier.