Since this was not clear for me, I decided to setup a small Wiki(*).
Basically I misunderstood the standart by assuming that any
mathematical operation on an image should lead to Secondary Capture. In
the case of ITK (Medical Toolkit), everything -well almost- is coming
from a scanner, therefore I can rewrite the output in DICOM using the
DERIVED Image Type. Which indeed seems to solve my problem with GE A/W.

Of course, any comment on the wiki is welcome,

Thanks to Steve Robbins for the initial link.