As we're all different, I think the official rules are there to make sure that everyone can succeed and there are no conflicts between how the bars, mousse and water flavourings could possibly affect our progress.
In practice, it is possible to bend these rules for some people. I am not saying that it is right and I am not saying that everyone should try it. But I've said it before and I still firmly believe that it is much better to have a bar, mousse or water flavouring on the same day if it means you aren't tempted by something else that isn't even allowed on CD. This will most likely affect some people, but will surely be a small price to pay if it prevents you from falling off the diet completely. Others won't be affected by it at all, so can then safely use what works for them to stay on track.
Earlier in the year I was on CD SS and I had 2 spoons of water flavour and mousse on the same day. Not just for one day, but for a whole week. On one of the days I had 2 mousse's and on 2 of the days I also had a bar. I still lost 6lb in that week, which was exactly the same as the week before when I had stuck much closer to the rules.
I have just restarted and I'm on day 5 of CD SS and I have been using 2 spoons of the water flavouring every day since day 1. I've also had 2 bars so far and will be having one this evening too.