Linking files (located outside project) to project relative to project directory path

Hello,

at the moment we are using mainly IAR Embedded workbench and now want to additionaly support CCE/CCS builds of our projects.

Our directory structure (which we don't want to change) hast several projects, that rely on a lot of common files (headers, c-source-files) which are maintained centrally outside the customer-specific files in the project directories.

Example structure with directories "includes/" and "common_sources/" outside the project directories.

|
|->project_1/
|       |->src/
|       |->project-files
|->project_2/
|       |->src/
|       |->project-files
|->includes/
|       |->headerfile_1.h
|       |->headerfile_2.h
|->common_sources/
        |->sourcefile_1.c
        |->sourcefile_2.c

How do I tell Code Composer for e.g. project_1 that it should also compile sourcefile_1.c?
In IAR I can use "Add files" which includes the files relative to the project directory in the form "../common_sources/sourcefile_1.c".

I tried to use "Project->Link Files to Active Project..." in CCE to do this, but this adds the absolute path to the files, not the relative path as I need it.
Because of this the build isn't working any more when the project structure is moved to a different location, e.g. during a checkout to a different directory or machine out of our versioning sytem.
I didn't have the possibility to try CCS up to now, so I am also very interested how its behaviour is.

For the include directories I use the Eclipse macro ${project_loc} to reference relative to the project path. For the above example this would be:
"${project_loc}/../include"

Does anybody know how to reference the source files relative to the project directory in CCE and CCS?
I hope there is a way to do this, as I regard this as pretty essential for a multi-build/multi-user enviroment...