Hi Markus,
you're planning layout and architecure is not clear to me.
You want to have one input query / web template where you enter workload for internals and externals?
If you don't want to mix your 0EMPLOYEE with ZEXTERN data, I would recommend to create a new dummy infoobject ZDUMMY which holds both 0EMPLOYEE and ZEXTERN data. Create two transformations/DTP for attributes from 0EMPLOYEE and ZEXTERN to ZDUMMY.
Then you need a real-time cube with ZDUMMY and workload keyfigure.
You can build a input ready query on top of it and enterworkload for all employees.
If you save data will be written back to real-time cube.
To have manual entries in ZEXTERN imemdialtely available you need real-time extraction of it (or at least regular schgeduled) uploads from ZEXTERN to ZDUMMY.
Regards,
Jürgen