How to improve the billing concept increasingly:
1. Make a selection of the projects including the option ALL projects
2. Make a selection of the billing period (from - to)
3. The result is a list of ALL projects and a drill down list of ALL billable hours (detailed like now)
4. All the hours are checked on, so you only need to uncheck the special ones
5. Export to report/ Datawarehouse

I think this works must easier than the other way around