We have finally discarded the use of user-exits to meet the requiremente: as the WO are copied by reference, the user should check (by clicking on the "General" button within the "components" tab) every single one of the components in order to trigger the user-exit.
Obviously, that is not feasible as some WOs include dozens of components.
At last, we have included the corresponding logic in an enhancement point of the standard FM that copies the components when a WO is created by reference through IW31.
Thanks and best regards,
J