I think I figured out a sort of work/around, but missing something 
When I use the advanced workflow edition, I'd like to place only the Zip / Post code field before the other fields,
so a customer needs a short time of effort to fill in the post code, afterwards, the system should show / log
this field and the custom field would be calculated.
So, the main question here is, how can I place a custom field (not the complete address package) in
the advanced workflow edition? I really think many customers could use such a thing (there are many things to
calculate / check before the actual checkout)
Hielke