I \'ve already solved the problem of getting the object id being edited using this code:
class CompanyUserInline(admin.StackedInline):
\"\"\"
Defines
As far as i know it is not possible to access the current instance through the formfield_for_...-methods, because they will only be called for a single field instance!
A better point to hook into this logic where you can access the whole instance/form would be get_form. You can also overwrite a form field's queryset there!