Compiling WidgetSet with more than one eclipse project

We have one application that is customized for every customer. Because of that our eclipse workspace consists of round aboput 7 projects. One project for the customization (it is also the main project which contains the UI class an so on), some projects for the basics and one project to capsulate all vaadin related stuff.
Everything works quite fine with the exception of compiling widget set. We are using some add ons (as jars) which are placed in our vaadin project. The widgetset itself is defined in the main custom projects. All add ons are in the classpath of the vaadin project and so on and the main project references the custom project. But when I compile the widgetset all add ons are ignored. I have to put the add ons to the classpath of the main project too than everything works fine.
But it is a little bit stupid. If we want to use new add ons, newer version or something like that we always have to adjust the classpath of all the custom main projects just for the compilation of the widgetset.
Are there any other possibilities? It would be great, if we only have to make some changes in our vaadin project.